Every actor has a particular type they can play well, for some reason or another. It doesn't necessarily have anything to do with who we are in real life, but it's just what we do well.
Example: Travolta is amazing as the Lovable Loser. When he's in Welcome Back Kotter and Saturday Night Fever in the 70s, he is the biggest star in the world, because people can identify with him in a way they may not be consciously aware of.
Then, in the early 80s, the industry decides to make him The Leading Man. They put him in films like Perfect and Urban Cowboy, and his career tanks. Nobody can connect to those characters, because it's not the right type for him to play. He does those talking baby movies for awhile, and then he explodes back to the top of the A list when he plays a junkie hitman in Pulp Fiction. He's back to being the Lovable Loser, and audiences go crazy for him, because that's the type he's meant to play.
So why do I play evil characters? When I was a kid, I played the sensitive, awkward kid full of self doubt who really wanted you to like him*. When I was in my 20s, I kept getting auditions for those roles and never booking them, because it's just not the type I'm meant to play. When Kim Evey cast me as a douchey agent in Gorgeous Tiny Chicken Machine Show, and Felicia wrote me into The Guild as douchey Fawkes, things started to turn around. I realized that I'd found my type, and I started looking for those roles.
It turns out that my type is the Villain You Love To Hate, so that's who I am in The Guild, Leverage, Eureka, and Big Bang Theory. I don't think it's a coincidence that, once I started playing these types of characters, my acting career began to come back to life, and I will be grateful for the rest of my life to Kim and Felicia for taking a chance on me.
I really don't know why this is my type, but whenever I try to figure it out, I start to feel like Lenny with the rabbit, and I really don't want to break something that's working out pretty well for me right now.
I do know this, though: the whole point of being an actor is to portray characters who are different from who you really are. The most important thing in the entire universe to me is kindness, so it's really fun to play characters who are antithetical to my personal ideals. Exactly why I seem to be so good at doing that, though? I'm not going behind that particular barn.
*Incidentally, that's pretty much who I've been in my real life since I can remember.