Doctor Who: 10 Worst Things The Master Has Ever Done
8. Allying Himself With The Daleks
The Master may be the Doctor's arch-enemy, but it's the Daleks who are the greatest foes of the Time Lords as a species. Hell, the Daleks killed more Time Lords during the Time War than it's possible to count, and they've been laser-blasting their way through the universe since the show's earliest days.
Because of this, it could almost be considered treason for the Master to team up with them, and yet... that's exactly what he did in Frontier In Space.
Late in this serial, the Master announces that he's been working with some "old friends" of the Doctor's, revealing that he has forged an alliance with the Daleks in order to instigate a war between the humans and the Draconians. This was intended to weaken both parties, making it easier for the Daleks to conquer the universe - something they're rather keen to accomplish.
If there was ever any doubt that the Master is a massive dick, then this serial proved it. He's perfectly fine allying himself with a race as vile as the Daleks, which tells you all you need to know about how little he cares for the universe, as well as the people in it.