Time Travel Synthesis

In Poul Anderson's Time Patrol series, the Danellians appear in different forms. At the beginning of his Patrol career, Manse Everard sees a blazing shape. Much later, he meets a benign humanoid being of indeterminate race, age or sex. In Doctor Who, the Time Lords periodically "regenerate." They are rejuvenated and their appearance changes, i.e., a different actor plays the part. Both groups are masters of time travel. Thus, could they be the same group? See here.

Is the Doctor's humanoid appearance a mere appearance? On TV, he once said that the TARDIS's appearance was here but that its real being was outside time. Another character commented, "Ah, you are a true philosopher!"

On its original publication in Tales Of The Knights Templar (New York, 1995), edited by Katherine Kurtz, the last Time Patrol story, "Death And The Knight," was doubly introduced by editor and author. Kurtz wrote that, if time is fluid and mutable, then we must hope that there are or will be Time Lords to perform policing tasks:

"...to make certain that crucial aspects of our past are not changed, so that all our yesterdays will unfold into our desired tomorrows...
"Poul Anderson writes of the Time Lords thus:..." (p. 273)

Anderson does not use the term "Time Lords" but, in this passage, he does not name the Danellians either. He writes of "...the superhumans who dwell in the ages beyond..." (p. 274)

There is much scope here for creative sequels.

The Bird of Time has but a little way
To fly — and Lo! the Bird is on the Wing.
-copied from here.

Future Histories And Time Travel

(Most of today so far has been spent driving back to Lancaster.)

Robert Heinlein
Heinlein's Future History was complete in five volumes but unfortunately he added three or four inauthentic novels. The first of these, Time Enough For Love, concludes with a time travel section, "Da Capo," that includes an ingenious passage on how Lazarus Long sends messages home from the early twentieth century but otherwise is appalling drivel. (I go further and add that at times Heinlein's later obsession with sex became frankly offensive.)

Isaac Asimov
Asimov's The End Of Eternity is an incoherent time travel novel (see here) that concludes by initiating the timeline of his Galactic Empire future history.

Poul Anderson
Anderson did not connect the Time Patrol to the Technic History but did connect There Will Be Time to the Maurai History.

However, in the Technic History, two characters present the germ of a time travel story. See here. Let us expand it:

the Marchwardens of the Lauran System have reason to expect an attack from the future and prepare defenses;
the attack arrives and is defeated;
five centuries later, the Merseians have a time machine and consider attacking the Lauran System five centuries earlier;
however, historical records inform them that that attack arrived and was defeated;
therefore, they do not launch the attack.

By the Time Patrol rules of time travel, this could happen. The cancellation of the launch of the attack cannot prevent the earlier arrival of the attack.

Time Travel Villains

Copied from here.

First, see here.

The Master's problem is how to disrupt and rule history without being stopped by extratemporal counterintervention. To get help, he travels in his TARDIS and rescues Merau Varagan, Raor and some Neldorian thugs from the exile planet. Seeking military intelligence, the Three (The Master and the two Exaltationists), helped by the Neldorians, abduct Manson Everard from his New York apartment, the Doctor from UNIT HQ and Captain Jack from Torchwood.

The Time Traveler has redesigned his Time Machine so that it can travel in any direction of space or time as originally intended. He spies on UNIT by traveling through its space-time in order to learn about the mysterious time traveler called the Doctor. Thus, he witnesses the appearance of the Master's TARDIS, the abduction of the Doctor and the TARDIS's disappearance. Traveling back in time and forward in space, the Time Traveler enters the TARDIS. He must now rescue the captives and help them to overcome the Three. He can travel through the space and time within the TARDIS as it travels through external space-time.