Avengers

In the Daft Dimension, when Marvel UK's Doctor Who Weekly was announced at a comics convention in 1979 by Dez Skinn, one of the Marvel fans in the audience asked if these Marvel-produced comics would see the Doctor join the Avengers. (COMIC: The Origin of Doctor Who Magazine)

Behind the scenes
The Avengers are a notorious team of Marvel-brand superheroes. The occasion of many internal crossovers within Marvel's titles, its roster boasted many of the superheroes belonging to Marvel at the time, hence the question of whether the Doctor might be shown to join the organisation, if he was to become a Marvel character in some sense.

Of course, this did not come to pass, though Marvel UK's stewardship of the production of original Doctor Who comics still saw the Doctor encounter several Marvel characters, including some who were elsewhere shown to be members of the Avengers; among them were the Hulk, Iron Man and Thor.