Thanos is a fictional supervillain appearing in American comic books published by Marvel Comics. The character, created by writer/artist Jim Starlin, first appeared in The Invincible Iron Man #55 (cover dated February 1973). Thanos is one of the most powerful villains in the Marvel Universe and has clashed with many heroes including the Avengers, the Guardians of the Galaxy, the Fantastic Four, and the X-Men.
The character appeared in the Marvel Cinematic Universe, portrayed by Damion Poitier in The Avengers (2012) and by Josh Brolin in Guardians of the Galaxy (2014), Avengers: Age of Ultron (2015), Avengers: Infinity War (2018), and Avengers: Endgame (2019) through voice and motion capture. The character has also appeared in various comic adaptations, including animated television series and video games.
Writer-artist Jim Starlin originally conceived of Thanos of Titan during college psychology classes. As Starlin described:
I went to college between doing U.S. military service and getting work in comics, and there was a psych class and I came up with Thanos … and Drax the Destroyer, but I’m not sure how he fit into it, just anger management probably. So I came up to Marvel, and editor Roy Thomas asked if I wanted to do an issue of Iron Man. I felt that this may be my only chance ever to do a character, not having the confidence that my career was going to last anything longer than a few weeks. So they got jammed into it. Thanos was a much thinner character and Roy suggested beefing him up, so he’s beefed up quite a bit from his original sketches … and later on I liked beefing him up so much that he continued to grow in size.
Starlin has admitted the character’s look was influenced by Jack Kirby’s Darkseid:
Kirby had done the New Gods, which I thought was terrific. He was over at DC at the time. I came up with some things that were inspired by that. You’d think that Thanos was inspired by Darkseid, but that was not the case when I showed up. In my first Thanos drawings, if he looked like anybody, it was Metron. I had all these different gods and things I wanted to do, which became Thanos and the Titans. Roy took one look at the guy in the Metron-like chair and said: “Beef him up! If you’re going to steal one of the New Gods, at least rip off Darkseid, the really good one!”
source : wikipedia.org