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Robert Downey Jr./Iron Man
One of Downey's first memorable roles was bully Ian in 1985's Weird Science. Thirty years later, he's still rocking the smarmy rich boy persona, only in a slightly more super-powered capacity as Tony Stark/Iron Man in the Marvel Cinematic Universe.
Before he picked up Mjolnir to play the hunky Norse god in the Thor and Avengers franchises, Hemsworth was a household name down under due to his three-year stint on Australian soap Home and Away.
Chris Evans/Captain America
Evans' first major role was alongside Milo Ventimiglia and Kyle Howard on short-lived Fox sitcom Opposite Sex. Before landing the role of Captain America, Evans had another turn as a superhero as Johnny Storm/The Human Torch in the mid-2000s Fantastic Four franchise.
Mark Ruffalo/The Hulk
Ruffalo didn't make his feature film debut until 1993, but early acting jobs included a hilariously goofy turn in a 1989 Clearasil commercial. The actor replaced Edward Norton in the role of Bruce Banner/The Hulk for 2012's The Avengers.
Scarlett Johansson/Black Widow
Sony Pictures Classics/Marvel
Johansson, who started acting at age nine, was nominated for an Independent Spirit Award for her leading role in 1996's Manny and Lo. She's played Russian spy-turned-Avenger Natasha Romanoff/Black Widow in the Avengers, Iron Man, and Captain America franchises.
New Line Cinema/Marvel
Renner's first film role was as a slacker the 1995 film National Lampoon's Senior Trip. He has played Clint Barton/Hawkeye in the Marvel Cinematic Universe since 2011's Thor.
The British actor landed a role in Stephen Whittaker's 2001 television adaptation of The Life and Adventures of Nicholas Nickleby (which featured Agent Carter star James D'Arcy in the titular role) when he was still doing student plays at RADA. His previous work with director Kenneth Branaugh helped him get the part of scorned little brother-turned-supervillain Loki in the Thor and Avengers franchises.
Samuel L. Jackson/Nick Fury
After a 1981 stage performance of A Soldier's Play, Jackson met Spike Lee who gave him small parts in his early films School Daze and Do The Right Thing before Jackson's breakout role in 1991's Jungle Fever. The legendary actor has portrayed S.H.I.E.L.D. director Nick Fury in the Marvel Cinematic Universe since 2008 and let the company use his likeness for the Ultimate Nick Fury.
Clark Gregg/Phil Coulson
Gregg guest-starred on Law and Order before landing memorable roles on shows like The West Wing, Will & Grace, and The New Adventures of Old Christine, but he is now best know for portraying S.H.I.E.L.D. agent Phil Coulson in five of the Marvel universe films as well as on ABC's Agents of S.H.I.E.L.D.
Cobie Smulders/Maria Hill
Before landing her most recognizable role on How I Met Your Mother, Smulders had several guest spots on procedural and drama shows like Fox's Tru Calling. Smulders has now portrayed Maria Hill in three Marvel movies as well as on ABC's Agents of S.H.I.E.L.D.
Elizabeth Olsen/The Scarlet Witch
Olsen plays the Scarlet Witch, twin sister to Aaron Taylor-Johnson's Quicksilver in the upcoming Avengers: Age of Ultron, ironic considering Olsen is the youngest sister to arguably Hollywood's most famous twins. Growing up, Olsen appeared in some of her famous big sisters' movies like The Adventures of Mary Kate and Ashley before her breakout role came in 2011's Martha Marcy May Marlene.
Taylor-Johnson worked steadily as a child actor before his breakout role in 2010's Kick-Ass. His first major movie role was 2002's Tom & Thomas.
The Blacklist star, who portrays the titular villain in Avengers: Age of Ultron, got his start in '80s teen fare like Pretty in Pink, where Spader played "richie kid" Steff.