2. Alexander Mahone (Prison Break)
When Agent Mahone was first introduced to Prison Break in Season 2 I'm sure many people thought he would be a by the numbers, easily dispatched adversary for Michael Scofield and co to outwit over the course of 20 or so episodes. But he quickly became one of the most deep and diverse characters in the entire show. Haunted by a decision to murder a criminal called Oscar Shales, Mahone is quickly revealed to be drug dependant and in possession of a fragmented family life he has no hope of getting back together. As the show progresses Mahone becomes more and more unable to hold it all together, his decisions and wrong-doings come back to haunt him and by the end of Season 2 he is incarcerated in Sona - the most awful prison on the planet. In here he battles drug withdrawal while trying to all himself with those he was chasing. William Fichtner gives an immense performance and while Schofield's savant-like intelligence remains captivating, it is the rock bottom Mahone hits which, to me, became more engaging. In Season 4 he suffers more tragedy when his son is killed and we continue to back him as he seeks revenge on the man who did it. Towards the end of Season 4 I feel like Wentworth Miller takes the ball back from him, but for a large part of Prison Break's run, Mahone was the more interesting of the two.