There was an old man with a beard, who said: 'It is just as I feared! Two owls and a hen, four larks and a wren have all built their nests in my beard.
You want to try and bring a character to life in an honest a way as you possibly can. It doesn't matter whether he's a doctor, an actor, a car salesman or a captain of a starship. If you can bring truth and honesty to that character, then your audience will believe you.