Let's see... He's ridiculously intelligent and charismatic, able to speak near-every language in existence even without his TARDIS, tougher than a normal human and able to resist most poisons, able to regenerate bodyparts and grievous wounds, able to Regenerate from death (instant reincarnation), technologically apt to the point of ridiculousness, especially when improvising... Low-level psychic abilities, enhanced perception of time and other dimensions... Sonic screwdriver, psychic paper, bottomless pockets...

One of the more important things, I think, is that he must be able to talk someone into suicide.