Earth-33⅓

Earth-33⅓ was a universe within which the Doctor and various other individuals apparently existed both as real people (COMIC: Doctor Who? 64, The Incredible Doctor Who History Tour (No. 7.), etc.) and as fictional characters in the series Doctor Who. (COMIC: Doctor Who? 87, Ever Wondered What Happened At.. The Auditions For The Seven Doctors?, etc.) Other series such as Star Trek were also known to exist in this universe, despite individuals such as James T. Kirk, Spock, and Beverly Crusher all existing as real people. (COMIC: Doctor Who? 176)

History
The Fifth Doctor landed his TARDIS in Madison Avenue during a crimewave, leading several superheroes, including Superman, Spider-Man, Batman, Captain America, and Jet Lagg, to enter the ship. This taught the Doctor not to land in New York during a crimewave. (COMIC: Doctor Who? 64)

More information to be added.

Behind the scenes
"Earth-33⅓" was the main universe shared by the majority of Tim Quinn and Dicky Howett's comic output, both to Doctor Who media, and to other Marvel media. Later Marvel guidebooks often refer to the universe as "Earth-333333333".