If you could remove a single Champion from the game, which one would it be and why?

I would honestly remove Karthus from the game. While some might disagree, I have yet to see anyone really master him as a whole. In ranked he is more of a feeder than an actual boon to the team. His kit is difficult for a lot of people to understand and a global ult that, though sometimes effective, doesn't really contribute all that much in the long run. Sure you get the one or two kills from nearly dead champs, but at the same time he really only has a slow and his mobility makes me cry. Mana hungry, difficult to use, and his kit is more selfish than helpful. Yeah... I'd say that's about the best I got.