The nature of acting means that actors are a chameleon - they disappear into a role, oftentimes playing a character who is totally unlike themselves. However, sometimes this means it can be very hard to separate the man from the role - we cannot see the man as anything but who he plays on TV. One substantial example is the actor Robert Knepper, who played "T-Bag" on Prison Break, and subsequent bad-guy creeps in shows like Breakout Kings and Stargate Universe. All of his major performances seem to be of morally unscrupulous, unforgivable villains, all with nefarious motives and unpredictable tempers.
However, if you see Knepper in interviews, he is revealed to be a kind, gentle, jovial man. At the same time, as I watch him on the screen, I cannot help but remember the last person T-Bag killed, or the steely gaze at the screen of a man who cannot be reasoned with. To that end, TV has the power to create perceptions of people that does not match who they really are. Even the impression you get from the "real" Robert Knepper does not override the sense of unease you feel about T-Bag. To that end, typecasting can be quite effective; it seems that one of the biggest reasons actors get typecast in the same kinds of roles is that executives, like the audience, just cannot see an actor as anything apart from their character. Knepper got his other bad boy roles after Prison Break because of T-Bag, just as the same is true of other actors.
