The Between the Pages blog tracked down the original set of five pitch documents for Doctor Who. It wasn’t until the fourth document, the Tom Baker of the group, that Doctor Who was explicitly mentioned by name.
The Secret of Dr. Who: In his own day, somewhere in our future, he decided to search for a time or for a society or for a physical condition which is ideal, and having found it, to stay there. He stole the machine and set forth on his quest. He is thus an extension of the scientist who has opted out, but he has opted farther than ours can do, at tne moment. And having opted out, he is disintegrating.
[Handwritten note from Sydney Newman: “Don’t like this at all. Dr Who will become a kind of father figure — I don’t want him to be a reactionary.”]
One symptom of this is his hatred of scientist, inventors, improvers. He can get into a rare paddy when faced witn a cave man trying to invent a wheel. He malignantly tries to stop progress (the future) wherever he finds it, while searching for his ideal (the past). This seems to me to involve slap up-to-date moral problems, and old ones too.
In story terms, our characters see the symptoms and guess at the nature of his trouble, without knowing details; and always try to help him find a home in time and space. wherever he goes he tends to make ad hoc enemies; but also there is a mysterious enemy pursuing him implacably every when: someone from his own original time, probably. So, even if the secret is out by the 52nd episode, it is not the whole truth. Shall we say:
The Second Secret of Dr. Who: The authorities of his own (or some other future) time are not concerned merely with the theft of an obsolete machine; they are seriously concerned to prevent his monkeying with time, because his secret intention, when he finds his ideal past, is to destroy or nullify the future.
[Handwritten note from Sydney Newman: “Nuts”]