Loki was introduced in Thor as the jealous younger brother of the titular hero, making moves to steal Asgard's throne.
Bucky Barnes made his debut in Captain America: The First Avenger as Steve Rogers’ (Chris Evans) kind and brave best friend.
Yondu (Michael Rooker) is introduced in Guardians of the Galaxy as Peter Quill’s (Chris Pratt) adoptive father.
Deadpool, aka Wade Wilson (Ryan Reynolds), starts as a mercenary for hire. In an attempt to cure his cancer.
Bruce Banner (Edward Norton in 2008, Mark Ruffalo onwards) never wants to be bad, but the green guy is a different story.
Nebula (Karen Gillan) is an adopted daughter of Thanos who was always pitted against her sister Gamora (Zoe Saldaña).
Lord M'Baku (Winston Duke) is the leader of the Jabari Tribe, a group of Wakandans who choose to live in isolation in the mountains.
Venom was introduced outside the MCU when he debuted as a villain in Spider-Man. Peter Parker is the first body he attaches himself.
Rocket (voiced by Bradley Cooper) is a scrappy, gun-toting member of the Guardians of the Galaxy.
Logan, or the Wolverine (Hugh Jackman), is the gruff, cigar-smoking mutant who is a favorite amongst X-Men fans.