Mr Smith

Mr Smith was a super-computer owned by Sarah Jane Smith who also served as one of her faithful allies. He was located in the attic of Sarah Jane's house at 13 Bannerman Road. He was actually a Xylok embedded into the computer. For a brief period of time, he was Sarah Jane's enemy, working with members of the Slitheen family to destroy Earth to release the other Xylok that had been trapped in the planet's crust for millions of years. (TV: The Lost Boy)

He was later rebooted with the sole purpose of protecting humanity. (TV: The Last Sontaran) Once K9 Mark IV returned to the group (TV: The Mad Woman in the Attic) Mr. Smith shared a rivalry with him over who best served as Sarah Jane's tech support, though they later got over the competition and were on good terms. (TV: The Nightmare Man)

Mr. Smith remained typically "off-line" until the phrase "Mr. Smith, I need you" was spoken; (TV: Invasion of the Bane - The Man Who Never Was) he would then activate, playing a fanfare for dramatic effect. (TV: The Stolen Earth) Though he could be programmed to not activate if Sarah Jane was not around, (TV: The Mark of the Berserker) or without the fanfare if asked "quickly and quietly" to activate. (TV: The Wedding of Sarah Jane Smith)

Origins
The computer known as Mr Smith housed a sentient and highly intelligent crystal known as a Xylok. In the distant past a Xylok spacecraft had crashed into the Earth, trapping the Xyloks in the crust of the planet. When the volcano Krakatoa erupted, one crystal escaped. Centuries later, Sarah Jane Smith retrieved the living crystal, took it to her home on 13 Bannerman Road, and found it could communicate with her via her laptop. The crystal informed her how to build the computer to house the living crystal. Sarah Jane did not know at this time about the Xyloks or that Mr Smith planned to free the other Xyloks, even at the cost of the planet itself. (TV: The Lost Boy)

Working for Sarah Jane
After she created the computer to house him, Mr Smith helped Sarah Jane, and offered her knowledge on many things. His help at this point however, was mainly confined to hacking other computers and displaying information on alien life forms. He momentarily revealed his dark side to Clyde Langer, presumably because he realised he might get help from the Slitheen. (TV: Revenge of the Slitheen)

Against Sarah Jane
Eventually, Mr Smith was able to team up with members of the Slitheen family on Earth. He helped two of them pose as Luke Smith's true parents so that they could kidnap him, but despite his efforts to separate Sarah from her allies, his deceptions were exposed when the Slitheens' fake history for Luke had too many holes for Maria and Clyde to accept it. Mr Smith attempted to prevent exposure by trapping Clyde within himself, but Clyde was able to pass on a message that warned others of Mr Smith's true agenda. While K9 kept Mr Smith distracted, Alan Jackson used a computer virus against Mr Smith which disabled him and wiped his database. As a result, Mr Smith forgot his purpose and asked for instructions. Sarah Jane informed him that his new purpose was to save the Earth, which he accepted and fulfilled thereafter. (TV: The Lost Boy)

Reprogramming
After his reprogramming, Mr Smith was of great help to Sarah Jane and Luke during the first part of the Dalek invasion of Earth in the 21st century. He alerted the Smith family to the Earth's changed position in space. He detected the presence of incoming space ships, and relayed the message of them to the Smiths. Once the fleet had been identified as Dalek in origin, he amplified an incoming sub-wave message from Harriet Jones. This message allowed a pivotal conference call between Sarah Jane, Martha Jones and Torchwood Three. They formulated a plan of action to contact the missing Tenth Doctor, in the hope that he could help repel the Daleks.

In this scheme, Mr Smith vitally linked together all the world's phone networks to dial the number of Martha Jones' phone aboard the TARDIS. Mr Smith's efforts were relayed to Torchwood, whose rift manipulator greatly amplified his signal. The power needed to amplify its phone call damaged the computer. Nevertheless, he was able to determine the site of the Doctor's TARDIS landing, prompting Sarah Jane to leave Luke in Mr Smith's care while she rendezvoused with the Time Lord. (TV: The Stolen Earth) Later, Mr Smith received the TARDIS base numerals from K9 and linked with the TARDIS and the Cardiff Rift, allowing the Doctor to tow the planet back to its proper place in space and time. (TV: Journey's End)

His on screen logo changed to a more fluid graphic and he developed a sense of humour. (TV: The Last Sontaran) Mr Smith told the team more about the Pied Piper including that he came from the Jeggorabax Cluster, but he needed more information so he asked Sarah Jane to go to the Pharos Institute to collect a part of the meteorite. (TV: The Day of the Clown) When Martin Trueman was possessing the world to join the Ancient Lights even Mr Smith became controlled and lost connection. (TV: Secrets of the Stars) He trapped threats with a containment vortex, for example, Mrs Wormwood. (TV: Enemy of the Bane) Using the sonic lipstick, he teleported a Slitheen back to Raxacoricofallapatorius. (TV: From Raxacoricofallapatorius with Love)

Mr Smith received a distress signal and video from a Judoon in a ship crashing to Earth. He told the gang where the ship was. Later on, Sarah Jane, possessed by Androvax, activated Mr Smith's self-destruct program, to destroy all of Bannerman Road in sixty seconds. Luke reminded Mr Smith that purpose was the most important thing to a Xylok and his purpose was to protect the Earth; Mr Smith's actions were against his purpose, so he stopped the countdown. (TV: Prisoner of the Judoon)

Feud with K9
Mr Smith helped Sarah Jane find Rani Chandra, who was in Danemouth, and then put Sarah Jane's phone through to K9 to use the black hole to power Eve's ship. This allowed K9 to come back. Mr Smith showed disdain for K9 very quickly. (TV: The Mad Woman in the Attic)

Mr Smith and K9 appeared to have had an antagonistic relationship with each other, attempting to one-up each other in the presence of Sarah Jane or the children. (TV: The Wedding of Sarah Jane Smith)

He showed a report on the disappearance of the Mona Lisa and told Sarah Jane that the painting which had Phyllis Trupp in it was the actual painting. (TV: Mona Lisa's Revenge) When the Slitheen-Blathereen gave Sarah Jane Rakweed, she had Mr Smith scan it. He found it harmless, but the morning after, the weed mutated and attacked Luke. When the spores threatened him and Sarah Jane, Mr Smith used his cooling air vents to suck them away. Mr Smith monitored Luke's condition during the crisis. When Clyde, Rani and K9 discovered how to stop the Rakweed, K9 sent Mr Smith the frequency level required to sound the alarm bell sound across London (1421.09 Hertz). He did this again when the two Blathereen attacked, causing the Rakweed in their stomachs to be destroyed, creating a build-up of methane gas which caused them to explode all over everyone, including Mr Smith. (TV: The Gift)

According to Luke, after humanity was transformed into the Master Race on Christmas Day, Sarah Jane got him to create a cover story, saying that Wi-Fi malfunctioned across the world and gave everyone mass hallucinations. (TV: The End of Time)

When the Nightmare Man put Luke into a deep sleep, Mr Smith used a USB cable to give K9 extra power to contact Luke. He was attacked and damaged by the Nightmare Man, but later recovered. Before K9 left to accompany Luke to university, Mr Smith told him that he could contact him if needed, which K9 took to mean Mr Smith would miss him. (TV: The Nightmare Man)

More adventures
When Androvax returned, Mr Smith trapped him in the containment vortex. (TV: The Vault of Secrets) When the Automatons removed all the humans from Earth except Clyde and Rani to look for the heir to the throne of their planet, Mr Smith was taken as well, leaving the computer an empty shell. He was returned when the Automatons found the heir. (TV: The Empty Planet) When Sarah Jane was secretly under attack by Ruby White, she asked Mr Smith to clear her voice from the command alphas. He still warned Clyde that Ruby was dangerous but was shut down by her, having fallen under the control of Mr White. After K9 reset Mr White, Mr Smith was restored and temporarily contained Ruby in a containment vortex before her escape. He later had Sarah Jane's voice restored to the command alphas and finally admitted K9 wasn't so bad. (TV: Goodbye, Sarah Jane Smith)

He was initially frightened of Sky Smith because of her tendency to blow up electrical devices such as him. (TV: Sky) As he was not human, he was unaffected by Hetocumtek's curse, helping Sky Smith work out what had happened. After he had helped Sky work out how to break the curse on Sarah and Clyde, he teleported the totem pole into the attic, where Clyde destroyed it, lifting the curse. (TV: The Curse of Clyde Langer)

Mr Smith was pleased that K9 did not accompany Luke when he returned from university. He told Sarah Jane the real Joseph Serf had died in a skiing accident in 2007 and analysed a SerfBoard with Clyde and Rani. They found out that it was a simple, low standard laptop. Luke used K9's whistle to speak to Mr Smith in Morse code, alerting Clyde and Rani to get the pen John Harrison was using to torture the Skullions. Luke and Sky took control of Serf whilst Sarah Jane and Adriana took the Skullions to the roof of the building. Mr Smith had alerted the Skullion species to send a spaceship to Earth to pick up the Skullions. (TV: The Man Who Never Was)

Later life
Sarah Jane and her gang continued to have adventures, defend Earth and save countless lives. Statues would be raised in their honour and they would leave behind a legacy that would last forever. (PROSE: The Wedding of Sarah Jane Smith, TV: The Man Who Never Was)

After Sarah Jane passed away, Mr Smith was sealed in the chimney stack on Sarah's introductions, leaving the house "waiting for the next owner" for new adventures. Mr. Smith mourned Sarah and agreed with Rani that Sarah was not really gone, instead believing she was off with the Doctor on new adventures. (WC: Farewell, Sarah Jane) Before he was sealed away, he gave Rani some holographic projection technology. (AUDIO: Hysteria)

Alternate realities
In Andrea Yates' World, as Sarah Jane died in 1964, Mr Smith was never sent to her, and the computer that housed the living crystal was never created. Nothing else is known concerning his fate. When Maria tried to call Mr Smith, the chimney stack that housed him is revealed to be an ordinary chimney stack. (TV: Whatever Happened to Sarah Jane?)

Frequently used
He possessed an extensive, but not absolutely complete database of alien life forms and could display them on his screen. (TV: Invasion of the Bane et al) At the behest of Sarah Jane, this database was later augmented with the Alien Files. (TV: Sarah Jane's Alien Files episode 1)

He secretly monitored the activity and communications of alien ships. (TV: Warriors of Kudlak)

Mr Smith played a fanfare of his own accord when activated (TV: Invasion of the Bane onwards) as shown when Sarah Jane Smith requested that he stop playing it during his activation following the transportation of Earth to the Medusa Cascade. (TV: The Stolen Earth) Luke Smith had also requested Mr Smith start in silent mode during Clyde, Rani, K9 and his attempts to spy on Sarah Jane. (TV: The Wedding of Sarah Jane Smith)

Mr Smith could relay messages from alien sources and display them on his screen. (TV: Invasion of the Bane, Warriors of Kudlak, Prisoner of the Judoon, TV: The Stolen Earth) He could scan alien objects in a drawer built into his computer such as telepathic stones. (TV: Death of the Doctor)

Less commonly used
He diverted meteorite K67 from colliding with Earth, using magnetic repulsion. (TV: Whatever Happened to Sarah Jane?)

He could digitalise a lifeform and store it inside him. (TV: The Lost Boy)

Mr Smith could also readily detect celestial bodies and ships in close proximity to the Earth, such as the other 26 planetary bodies and the Dalek fleet located in the Medusa Cascade. (TV: The Stolen Earth/Journey's End)

He could tap into every phone network on Earth. (TV: The Stolen Earth) The computer seemed to have heavy armaments, including projectile weapons. (TV: The Lost Boy) Mr Smith was also capable of entrapping alien threats within a containment vortex and sapping their weapons of their energy. (TV: Enemy of the Bane, The Vault of Secrets, Goodbye, Sarah Jane Smith)

Mr Smith had a tracking device with an aerial satellite scan. Luke, Rani and Clyde used it to track down Sarah Jane when she was meeting Peter Dalton. (TV: The Wedding of Sarah Jane Smith)

Mr Smith also had a self destruct setting which was capable of destroying the whole of Bannerman Road. This was activated by the Veil Androvax when he possessed Sarah Jane's body. When Clyde, Rani, Luke and Captain Tybo found traces of Androvax in Sarah Jane's House, Mr Smith warned them to leave as soon as possible as the house would blow up in 60 seconds. (TV: Prisoner of the Judoon)

He could be used to contact K9 inside the black hole. (TV: The Mad Woman in the Attic)

He had an air ventilation system with large fans hidden under his computer screen. (TV: The Gift) He could give K9 extra power via USB cable. (TV: The Nightmare Man) He could disable Mars Rovers and possibly other craft. (TV: The Vault of Secrets)

He had a "medi-scan" that could perform a full medical analysis of a subject. (TV: The Gift, The Vault of Secrets, Goodbye, Sarah Jane Smith, Sky)

He had a "voice remover" that could remove voices from the system so that certain people could not access him. (TV: Goodbye, Sarah Jane Smith)

He could tap into the teleports of alien ships that are on or close to Earth and use them for Sarah Jane's purposes. (TV: The Gift, The Curse of Clyde Langer)

He could use an energy reversal beam to reverse an enemy's actions back upon them and their teleports. (TV: From Raxacoricofallapatorius with Love)

He could communicate with other planets for various purposes including calling for teleports and rescue. (TV: The Wedding of Sarah Jane Smith, The Man Who Never Was)

He could pick up transmissions on all frequencies including K9's command frequency over great distance even when coming from just a dog whistle. (TV: The Man Who Never Was)

He could make replicas and duplicates of things such as the black diamond of Earnfield. The museum staff did not realise the difference between the replica and the original. (AUDIO: The Time Capsule)

Clyde and Luke played a video game about the Battle of Waterloo on Mr Smith's screen using futuristic controllers that Sarah Jane had acquired from a Wallarian Trader. (TV: The Last Sontaran)

Personality
Initially, Mr Smith comported himself with a cold, clinical mindset, more like an actual computer than a living being. When his true intentions were revealed, he acted maliciously and cruelly, becoming extremely ruthless and megalomaniacal, yet justified his actions by stating they were part of his "purpose". As such, Mr Smith was sociopathically logical and had no complaints about mass-murder or causing people who were thought to be his friends immense pain and suffering. He was even capable of a sadistic laugh, in spite of the fact that he was meant to be a computer, showing that he was actually a living being in crystalline, later electric, form. (TV: The Lost Boy)

After his memory had been wiped by the Armageddon Virus, (TV: The Lost Boy) Mr Smith's personality changed greatly. He became much friendlier and more amiable. He would make jokes. He bade Maria a fond farewell when she left for America. (TV: The Last Sontaran) After Sarah Jane's death, Mr Smith was shown to be as saddened by her loss as the rest of her friends. (WC: Farewell, Sarah Jane)

He showed great compassion for Sarah Jane's younger friends, especially her son Luke. He vowed to protect him from the Daleks (TV: The Stolen Earth) and did everything he could to save him from the Rakweed. (TV: The Gift), He also showed great concern for Sarah Jane after her heart was broken by Peter Dalton and the Trickster. (TV: The Wedding of Sarah Jane Smith)

When K9 returned to Bannerman Road, Mr Smith entered into a deep rivalry with him, the two constantly trying to one-up each other in the technical support, and referring to each other as "the dog" and "that computer". (TV: The Wedding of Sarah Jane Smith et al) However, when it appeared K9 was broken, Mr Smith refrained from calling him a dog and even expressed concern. Before K9 left with Luke for Oxford University, Mr Smith told K9 that he could call him if needed, which K9 took to mean he would miss him. Mr Smith didn't deny it, just telling K9 goodbye. (TV: The Nightmare Man) However when around others he still maintained his animosity for "the dog" though after K9 saved him from Mr White he finally called K9 by name and admitted he wasn't so bad, saying he'd met worse. K9 returned the sentiment. (TV: Sarah Jane's Alien Files episode 3, Sarah Jane's Alien Files episode 4, TV: Goodbye, Sarah Jane Smith) Despite this, he was still pleased when K9 didn't return with Luke from Oxford, showing there was still a rivalry between the two supercomputers. (TV: The Man Who Never Was)

He originally feared Sky due to her shorting out the power, but he got over it. (TV: Sky)

Despite his intelligence, Mr Smith could be literal-minded, such as when he gave Sky Smith information about the general details of school life while skipping over relatively minor information, so she thought that "toad-in-the-hole" actually had toad in it. (TV: The Curse of Clyde Langer)

Behind the scenes

 * It is not until Sarah Jane complains about it in The Stolen Earth that Mr Smith's fanfare is actually acknowledged as being something the characters hear, rather than incidental music for the viewer's benefit. The Wedding of Sarah Jane Smith establishes that it's possible to avoid the fanfare when Luke says he needs Mr Smith "quickly and quietly."
 * A possible reference to Mr Smith appears in the K9 story The Bounty Hunter. A news report in 2050 mentions that a "Mr Smith" won the National Lottery, but no one seems to know his first name or even who he is, and asks for Smith to step forward and accept his winnings.
 * The unproduced fourth story of series 5, Meet Mr Smith, would have featured Mr Smith becoming a human. It would later be revealed that this was due to an alien named Ozmo, who planned to use Mr Smith to capture Earth and its resources.