So hard to choose just one, but here are three of my favorites and why...
1. "The Mechanic" in Smilla's Sense of Snow by Peter Høeg. Because he is the type of man I wish there were more of in the world. A man who isn't afraid to nurture those weaker than himself, and fight those who are stronger.
2. Zaphod Beeblebrox from the Hitchhiker's Guide to the Galaxy series by Douglas Adams. If there was ever a creature who knows what fun is, it's Beeblebrox. Since I personally have so much trouble having fun, I stand in awe of Beeblebrox's attitude.
3. Manlius Hippomanes from The Dream of Scipo by Iain Pears. This character is the only fictional representation of myself I've ever seen -- and I read a lot of fiction. He's my ancient Roman twin. I couldn't believe it when I encountered him!