Adam Mitchell was a young English researcher in the employ of the American GeoComTex billionaire Henry van Statten in the year 2012. He was briefly a companion to the Ninth Doctor. After being abandoned by him, however, he later plotted to kidnap companions from every incarnation of the Doctor.

Adam was a genius who had 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 to work for GeoComTex. The Ninth Doctor and Rose Tyler met Adam in the year 2012. At the time he worked in van Statten's Vault in Utah, where he catalogued 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 with Rose. He told Rose that he had always wanted to see the stars; she asked the Doctor to take Adam along with them in the TARDIS. Rose also found Adam attractive. Despite the Doctor's scepticism about Adam as a potential fellow traveller, he agreed.

Adam's travels with the Doctor and Rose did not last long. Visiting the year 200,000, Adam was overwhelmed by the wealth of information and technology available to him and immediately gave in to temptation and greed. Desperate to gain all the information that the Fourth Great and Bountiful Human Empire had collected, he learned that only those with an implant could access the data. He had a top-of-the-line computer interface port, an infospike, installed in his head. When the implant activated to access computers, his head opened up, revealing part of his brain. The implant was activated by a snap of the fingers. He tried to transmit information back to 21st century Earth with Rose's superphone.

When Adam tapped into the computer systems, he inadvertently gave the Jagrafess knowledge of — and nearly access to — the TARDIS. One of Satellite Five's journalists, Cathica, freed Adam, prevented the Jagrafess from obtaining the TARDIS key and vented heat to Floor 500, killing it. Learning of Adam's transmission of information and his additional breach of trust, the Doctor angrily returned Adam to his home, despite Adam's apologetic pleading. The Doctor destroyed the answering machine which had received the information from the future. He observed that Adam would have to live a quiet life, lest someone discover the implant in his head and dissect him to find out where it came from. After the Doctor and Rose left, Adam was met by his mother who, when talking to him, clicked her fingers. As his head opened up, a look of shock and horror appeared on her face.

Biography from the TARDIS Data Core article, licensed under CC-BY-SA