Thanos (UK: /ˈθænɒs/, US: /-oʊs/) is a fictional comic book supervillain appearing in publications by the American publisher Marvel Comics. Created by writer/artist Jim Starlin, the character 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, the X-Men, among many others.

The character appears 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 the fourth Avengers film (2019) through voice and motion capture. The character has also appeared in various comic adaptations, including animated television series, arcade, and video games.