The only time Thanos is referred to by his nickname, the Mad Titan, in the Marvel Cinematic Universe is during Guardians of the Galaxy, when Corpsman Dey describes Gamora as being the “adopted daughter of the Mad Titan, Thanos.” Otherwise, he’s simply Thanos, the big purple guy who wiped out half the universe (before it was eventually reversed). Behind the scenes, though, the folks at Marvel had two different names for Thanos, one for Avengers: Infinity War and another for Avengers: Endgame.
In the new book The Art of Marvel Studios’ Avengers: Endgame, which features “concept art and exclusive interviews” and “showcases the work behind the culmination of 22 interconnected films,” concept artist Wesley Burt revealed that in Endgame, Thanos was known as “Warrior Thanos,” while in Infinity War, he was “Philosopher Thanos.”
This is Philosopher Thanos, content after accomplishing his mission.
This is Warrior Thanos, shortly before he gets wrecked.
Tag yourself.
Anyway, although Thanos died in Endgame, he’s not actually, well, dead. One of the deleted scenes from Endgame on Disney+ shows an alternate version of the Hulk’s interaction with the Ancient One. Basically, she tells him that no one was murdered in the original “Blip,” they were “willed out of existence,” which is not the same thing as having X’s for eyes. That leaves the door open for Thanos to return in further films, although probably not for a while, if ever. There’s a Multiverse of Madness to deal with first.