The Genesis of Doctor Who.

“A frail old man lost in space and time. They give him this name
because they don’t know who he is. He seems not to remember where he
has come from; he is suspicious and capable of sudden malignance; he
seems to have some undefined energy; he is searching for something as
well as fleeing from something. He has a ‘machine’ which enables them
to travel together through time, through space, and through matter.”

The Genesis of Doctor Who.