Doctor Who: What Happened To Every Companion?
4. Christopher Eccleston Era
After almost 20 years off the air, in 2005, Doctor Who burst back onto the BBC with a brand new season and a budget actually worth a damn. Now led by the venerable Christopher Eccleston, they explained the long absence of The Doctor was due to The Time War, a massive conflict between The Time Lords and their immortal enemies the Daleks. Which The Doctor was left as the last man standing. They wouldn't even wait 15 episodes before going back on this, but whatever.
The first companions of the new Who were Rose Tyler, Adam Mitchell, and that beautiful babyface bastard Captain Jack "you know you love him" Harkness. However, only one companion left this season, and Adam kinda had it coming.
Adam was a brilliant hacker who hacked into the US Department of Defense database for funsies when he was 8. His adventures with The Doctor only lasted one episode, as when The Doctor took him and Rose to the future, he quickly gave into the temptation and greed of the technology around him. He allowed his brain to be augmented with an implant that will let him tap into the computers, where he then used Rose's phone to try and transmit the information back to his time. The Doctor, enraged by the betrayal, dropped him back on his home world.