Douglass is the book's narrator, and it's a book about him. So in a way, it's hard to really describe him as a character. The entire book describes him as a character. But his personality is also where everything starts. Douglass is a titanic person, a real giant of a man, who persevered through some of the worst kinds of personal circumstances and never let his troubles and adversities take away his humanity. He doesn't just want to get by in this world; he wants to be great.
When the book starts, Douglass is still a child, and he's like most children: sort of oblivious, a little careless, and often getting into trouble. But, like most slaves, he also has no choice but to mature very quickly.
By the time he's a young teenager, in fact, he's dealing with some very adult problems. He's facing adversity in a way we come to expect from him as we get to know him better: he's always clever and resourceful in the face of danger, but forthright and unbending when it comes to questions of morality. Most young slaves learn to give in to the pressures of a hard life, learn to save themselves by going with the flow. But Douglass refuses to bend, to compromise his principles, or to ignore what he knows in his heart is right.
He's probably lucky that his stubbornness didn't put him in an early grave, but then maybe he's also lucky that he was so stubborn. Without that persistent courage, he never would have found his way north to freedom. But finding this balance isn't something that comes easily for him. The older he gets, the more Douglass gets singled out as a stubborn slave, so unyielding and determined in what he feels is right that he's seen as a threat to the whole system. From a very young age, he sees slavery as immoral, and he's not afraid to say so.
On the other hand, Douglass never has any desire to be a martyr. It's important to remember that he only puts his life on the line when he has nothing to lose. Douglass wants to live a full, normal live, and, though he is a crusader and an activist, he isn't a saint. He just wants what white Americans take for granted: life, liberty, and the pursuit of happiness.
Douglass is neither particularly social nor antisocial. He has a few friends, but he also understands that he has to leave his friends behind to become free. It is hard, but he does it. He always puts morality ahead of any other consideration, and his struggle to be free (and to free others) always takes precedence over everything else. As he put it in his later years, "I would unite with anybody to do right and with nobody to do wrong."