Rusty (Into the Dalek)

"Rusty" was the name given by the Twelfth Doctor to a Dalek captured by the forces of Combined Galactic Resistance, due to the outer Dalek shell being old and damaged. Intrigued and worried by Rusty's desire to exterminate the Daleks, the Doctor decided to explore the possibility for a "moral Dalek".

Early life
According to the research of human historians, Rusty was a Dalek fighting towards the end of the Dalek Wars. (PROSE:  The Astounding Untold History of the Greatest Enemies of the Universe) However, Rusty also knew about post-Time War events, implying he was actually a member of the New Dalek Paradigm. (TV: Into the Dalek)

Rehabilitation
Rusty lived a normal Dalek life, until one battle left him drifting alone in the depths of space; unknown to him, his power source had cracked and was leaking radiation that disrupted his shell's programming to keep him from feeling anything but xenophobic hatred towards non-Daleks. Seeing the birth of a star triggered a realisation in Rusty of the inevitability of life returning despite the efforts of the Daleks. From this, Rusty saw Daleks were evil and needed to be wiped from existence.

Eventually, he was found by the Combined Galactic Resistance, and brought aboard their ship the Aristotle. They attempted to open the shell, hurting Rusty. Badly hurt already, Rusty asked for help in recovering so he could exterminate his own race. Interested in the idea of a moral Dalek, the crew promised him medical attention.

The Doctor, Clara Oswald, Journey Blue, Ross and Gretchen Carlisle were shrunk and ventured into Rusty to try to fix the damage that was killing him. Using his sonic screwdriver, the Doctor repaired a crack in Rusty's power source that was leaking radiation and killing him.

However, without the radiation affecting him, Rusty reverted to his original Dalek programming, restored to full power and went on a rampage, killing several soldiers and sending a distress call that attracted a nearby Dalek flying saucer. Upon urging from Clara, the Doctor decided to attempt to restore the changes once more. He had Clara reactivate the Dalek's suppressed memories so he could see the birth of the star again and be reminded of the universe's beauty.

Clara succeeded and the Doctor telepathically linked with Rusty to show him more from inside his own mind. At first it seemed the Doctor had succeeded, as Rusty again saw beauty and divinity. However, Rusty also saw the Doctor's hatred of the Daleks, which resonated even more strongly with him. Rusty saw the Daleks as an evil which must be, in true Dalek fashion, exterminated.

Rusty then went on a rampage against his own kind, slaughtering the Daleks attacking the Aristotle and fooling the saucer into retreating by falsely telling the other Daleks that the Aristotle's self-destruct had been activated. Rusty left with the Daleks to continue his efforts against them, telling the Doctor that although Rusty himself was not a "good Dalek", the Doctor was a good Dalek. (TV: Into the Dalek)

Crusade against the Daleks
According to the human historians, Rusty's betrayal sent the Supreme Council in a world of worry, but their experiments proved that his freak turn of heart could not be mass-replicated. Relieved, and unwilling to snuff out such beautiful hatred as Rusty's, they consigned him to the Dalek Asylum, home to Daleks whose hatred was so powerful it threatened their own kind in one way or another. (PROSE:  The Astounding Untold History of the Greatest Enemies of the Universe) The asylum was ultimately destroyed by the Parliament of the Daleks. (TV: Asylum of the Daleks)

Based in Villengard
Rusty continued to fight the Daleks for billions of years. He isolated himself at the centre of the universe, in the ruins of Villengard, combating numerous Daleks that came to fight him. Rusty fended them off, positioning himself in a tower overlooking the battered city. The Twelfth Doctor, nearing his death, came to the lone Dalek with his original incarnation to gain information on the Testimony, as Rusty still had access to the Daleks' Pathweb. Rusty attacked him. However, he eventually removed his Gunstick as a peace offering to the Doctor, who persuaded him to help as it would irritate the Daleks greatly. After providing him the information he desired, the Twelfth Doctor left Rusty. (TV: Twice Upon a Time)

Legacy
After the Twelfth Doctor's mind was connected to a mind scythe, the "holiday snaps" the Doctor showed Kygon Brox included Rusty. (COMIC: The Instruments of War)

The Doctor remembered what Rusty had said to him when Missy offered him an army of Cybermen for his birthday that he could use to rule the universe. (TV: Death in Heaven)

Prop
Rusty was depicted using a bronze Dalek prop originally created for use in Asylum of the Daleks before being reprised in The Day of the Doctor and the Doctor Who: 50 Years.

Other matters

 * This was the fourth of four television individual Daleks to realise the evil of his kind and turn on them: the others are Metaltron (TV: Dalek), Dalek Sec (TV: Evolution of the Daleks) and Dalek Caan. (TV: Journey's End).
 * He is also the third televised Dalek to recognise the Doctor's potential as a Dalek himself. In Dalek the single Dalek having heard the Ninth Doctor's hatred and anger told him "You would make a good Dalek".
 * The Doctor and the Dalek, which like Into the Dalek was also credited to Phil Ford, features a Dalek which the Doctor names Lumpy who shares many similarities with Rusty (though unlike Rusty, Lumpy permanently reverts to his baseline "evil" self by the end of the game).
 * Rusty was also seen to fight the Daleks with the Doctor and in the GAME: LEGO Dimensions.
 * Originally Rusty was planned to blow up on the Dalek ship. This ending can be seen in an early black and white version of the episode, which leaked online before the original episode's release.
 * Rusty appears briefly in the webcast Merry Christmas!, decorated like a Christmas tree and carrying a sign that reads MERRY CHRISTMAS.