Doctor Who: 7 Times The Doctor Was Betrayed By Their Companions

7. Adam Mitchell Exploits Knowledge Of The Future

From Susan, Ian, and Barbara, all the way through to Graham, Ryan, and Yaz, most Doctor Who companions - even the less popular ones - have their fans.

But Adam Mitchell, on the other hand? Well... even the most stubborn Whovian probably couldn't bring themselves to side with him.

A short-lived companion to the Ninth Doctor, Adam's temporary TARDIS tenure came to a tense conclusion when he betrayed the Doctor's trust for nothing more than personal gain. Exploring Satellite 5 in the year 200,000, Adam's greed prompted him to try and collect as much future knowledge as he could - mainly technological knowledge - so that he could send it back to his own time.

Basically, just imagine a caveman trying to steal the blueprints for a MacBook.

Upon discovering Adam's meddling, the Doctor, naturally, grew quite angry. As he puts it, just "one second" of that knowledge could change the world for the worse, severely disrupting humanity's natural technological progression.

As a result, the Doctor dropped Adam off in the 21st century, dumping him from TARDIS duties forever. In the show, this is the last we saw of the character, but in the comics, Adam goes on to become a full-fledged villain, seeking vengeance against the Doctor for leaving him behind.