I think melee warrior tank, could do it easily. My melee char has like 70% block chance, all resist more than 100, ~170 armor rating, 1500 hp (on hard), 5 willpower, 5 bodybuilding, and he still can do enormous damage. He can only be killed if enemies are lucky enough to cc him for at least 5-6 turns, and don't use any elemental attacks, which would heal him instead of damaging.
If I had lone wolf on him, and gave him every book I've obtained from teller of secrets, I'm pretty sure he could win even vs all bosses from the game together.
