Adam Mitchell

Adam Mitchell was a young English researcher in the employ of the American GeoComTex billionaire Henry van Statten in the year 2012. He was very briefly a companion to the Doctor.

Biography
Adam was a genius, having successfully hacked into the United States Department of Defense computers when he was eight years old, nearly causing, in his own words, World War III. He was recruited by Van Statten. The Doctor and Rose Tyler first met Adam in his early twenties. He worked at the time in Van Statten's Vault in Utah where Adam cataloged extraterrestrial artefacts for his employer. When the Dalek Van Statten had "collected" got loose and went on a rampage, Adam found himself running from it along with Rose. At the end of this adventure, Rose asked the Doctor to take Adam along with them in the Doctor's TARDIS as Adam had told her earlier that he had always wanted to see the stars. Rose also found Adam attractive. Despite the Doctor's scepticism about Adam as a potential fellow-traveller, he agreed (DW: Dalek).

Adam's travels with the Doctor and Rose would not last long. Visiting the year 200,000, Adam was overwhelmed by the wealth of information and technology available to him and ultimately gave in to temptation and greed, desperate to gain all the information that the Fourth Great and Bountiful Human Empire had collected, but discovered that only those with the infospike implant could access the data. He had a top-of-the-line computer interface port known as an infospike installed in his head. Unfortunately for 21st century sensibilities, when the implant activated, his head opened up, revealing part of his brain. The implant was activated by a snap of the fingers so he could access the future's computer systems and attempted to transmit information back to 21st century Earth using Rose's "Superphone". (Along with the interface port he also got the Vomit-O-Matic for free.)

When he discovered this breach of his trust, the Doctor angrily returned Adam to his home despite much apologetic pleading and destroyed the answering machine which had received the information. The Doctor observed that Adam would have to live a quiet life from now on, lest someone discover the implant in his head and dissect him to find out where it came from. After the Doctor and Rose departed, Adam was met by his mother who, when talking to him, clicked her fingers. When his head opened up she had a look of shock and horror on her face. (DW: The Long Game)

Behind the scenes

 * Disregarding one-off companions, Adam Mitchell is the only companion from the revived series not included in DW: Journey's End the finale to Series 4 of Doctor Who. Adam is also the only companion of the Ninth Doctor not also to be a companion of the Tenth Doctor. He is also the only companion to be kicked off the TARDIS just one episode after joining the Doctor.
 * Adam is the only known companion to be actually expelled from the TARDIS crew due to bad behaviour.
 * In 2005, the website "Who is Doctor Who?" announced that 14 year old Adam Mitchell had won a competition arranged by Van Statten the previous week. Adam's winning essay on "Why I Want To Meet An Alien" focuses on acquiring advanced knowledge from them ("I don't think it's cheating, really. It's just a shortcut"), foreshadowing both his work for Van Statten and his actions later.
 * Adam is a member of that small group of companions who had no scenes in the TARDIS interior. He is seen entering and emerging from the TARDIS several times but he is never seen within the TARDIS itself. Like him, Harry Sullivan was never given an interior TARDIS scene — mainly because there was no budget for refurbishing the control room set that season.  Also, Liz Shaw wasn't shown to even enter the TARDIS, much less travel in it. On the other hand, she did at least have a scene with the console, when it was removed to the Doctor's temporary lab in Inferno. And, depending on one's definition of "companion", Astrid Peth, Christina de Souza and Adelaide Brooke never got an interior TARDIS scene, either — though at least Brooke got to ride in the TARDIS once.  Interior TARDIS scnes were, in fact, comparatively rare during certain eras of the programme, so Adam's plight isn't that unusual.