Now the most important part of every Dr that has ever been and will ever be is his eccentricities, change anything else you like, but that one thing must remain.
The Dr is half human (his mother's side), has two hearts and is a Time Lord with a semi-working T.A.R.D.I.S., the cloaking function is stuck in the police box mode, but he refuses to get it fixed (sentimentality).
The Time Lords seem to be the self appointed protectors of time. There to guide anyone from making the same mistakes they once did. And as a Time Lord the Dr can regenerate, which is to say if he dies, his body will repair itself and morph into another. The very last incarnation of the Dr is supposedly The Master, who is the Dr's worst enemy, supposedly trying to bring about his own creation by killing his previous incarnations.
By knowing that he becomes The Master in the future means that he obviously knows that whatever his current state is, isn't his last and knows nothing bad will happen to him. This and the fact he has a T.A.R.D.I.S. which is the most desirable form of transport ever, allowing to travel wherever and whenever he chooses instantaneously. Plus the fact that he understands how it works and species throughout the galaxy have killed to try and get that knowledge, gives his personality a certain dottiness, but also a streak of resolve and certainty.
The Dr is the most interesting character in the whole of Sci-fi with a deep past, eccentric present and tragic future. You could be mistaken in thinking that he would be feared because of his power, but instead he is hated and hunted through time and space by powerful enemies. Through each episode we see this and yet we never know quite what will happen in the lives of the people around him. I just hope the production team don't screwup the Daleks.