Not in a comic book.
Not played by Josh Brolin in an "Avengers" movie.
Nope. Thanos in a paperback novel: "Thanos: Death Sentence" by Stuart Moore.
Well, kinda Thanos.
He's Thanos – the expected Thanos – in the opening pages.
Thanos possesses the Infinity Gauntlet again.
He wipes out all of the Marvel heroes, worlds, etc. Marvel movie watchers may be surprised to learn that in the comics, and apparently in paperback novels, Thanos is hard to kill even when he's dead and he repeatedly attains the Infinity Gauntlet.