The "Captain Ersatz" trope refers to characters that are blatant stand-ins for other characters. Professor Gamble is Marvel Comics' Captain Ersatz for Doctor Who.
Professor Justin Alphonse Gamble was a member of Time Variance Authority, but quit the TVA and stole one of their time machines. He battled rogue Time Variance Authority robots called "Incinerators" (Dalek stand-ins). Using the name "Sergius O'Shaughnessy", he penned Day of the Dredlox, a Broadway play that glorified himself (which used his real name in the play). He helped Iron Fist and Luke Cage when they were stuck in the wrong time and being attacked by the Incinerators. Using a mini-Incinerator, the Incinerators broke in, took over his time machine and captured Gamble. They read his mind. Wanting to build a machine that would destory time itself, they went back to the time of Camelot to get the Starstone, which they need to built it. The Anachronauts freed Gamble. Gamble retook control the machine and expelled the Incinerators. Gamble set off to give Merlin the Starstone.
Powers and Abilities
Professor Gamble is genius inventor and thinker. He claims to be 95. If this is true, he would age slower than normal people. His time machine's exterior appearance is altered to make it seem like it is from the time period he is in. It is also bigger on the inside.