One of my favorite types to play is the apparently upright guy in a position of authority who turns out to be deeply flawed, intensely and dangerously psychotic and devious, or at least a sociopath. Those are some of the most fun roles. The somebody's-dad or cool-uncle or sidekick roles are cool, in a mellower way. But, it is always more fun and challenging to sort of lay behind the log in the plot, blending in, until a twist happens that reveals how sinister my character really is, and no one ever saw it coming.