3) The Mandarin
Comic Books: The archenemy of Iron Man from the beginning of the character’s lifespan, the Mandarin is a Chinese crime lord with ambitions of world domination. He’s most known for his ten rings: derived from a crashed alien spaceship, each one gives the Mandarin a different energy and light based power. He’s also a formidable martial artist and a genius-level scientist.
MCU: Oh boy, where to start? Initially in Iron Man 3, it looked like Marvel had reimagined the Mandarin as a self-styled terrorist who had appropriated Chinese culture. It was later revealed, however, that Ben Kingsley’s character was an actor employed by “the real Mandarin” – Tony Stark’s old business rival Aldrich Killian (Guy Pierce), who had gained superpowers from the Extremis drug.
Due to the negative backlash against the movie’s treatment of the supervillain, however, it was later revealed that a more comic book accurate Mandarin is still out there. Maybe he’ll turn up for real one day…
2) Bucky Barnes
Comic Books: Just like Batman had Robin, Captain America had Bucky Barnes. The plucky young sidekick aided Steve Rogers in his adventures throughout World War II…until he was believed to have been killed during a battle with Baron Zemo. Decades later – in real and comic book time – Bucky was revealed to have survived and been brainwashed into becoming the Winter Soldier, an assassin for the Russians. His old friend later cures him and Bucky goes on to briefly take on the mantle of Captain America.
MCU: While movie fans will recognize that Bucky’s Winter Soldier story is largely the same (just swap HYDRA with the Russians), it’s the character’s early years that are very different. Instead of his kid sidekick, Sebastian Stan’s Bucky is presented as Steve’s best friend of the same age. He also doesn’t operate as Rogers’ sole crime-fighting partner but is one of Cap’s team of Howling Commandos. As for Bucky’s future, it’s possible that he could become Captain America one day, but that hasn’t been either confirmed or denied by Kevin Feige and his crew just yet.