When Iron Man was released in 2008, few could've predicted that it would be the catalyst for one of the most successful entertainment franchises in history - the Marvel Cinematic Universe. Despite lacking the film rights to some of their most iconic characters, including Spider-Man and the X-Men, Marvel Studio's writers and directors, many of whom were somewhat left-field choices for their roles, have succeeded in creating a shared universe that continues to wow audiences with each subsequent entry. The series is already the second highest-grossing film franchise of all time, and needs just to make an additional $600 million at the box office to take the top spot from Harry Potter, which it will surely do when Avengers: Age Of Ultron (the trailer for which was recently showcased) is released on the May the 15th next year. Aside from the second Avengers outing, there are ten additional films that have already been announced, including new outings for Thor, Captain America and the Guardians Of The Galaxy, a further Avengers two-parter and standalone films for Ant-Man, Doctor Strange, Captain Marvel, Black Panther and the Inhumans. This is in addition to two network television series and five that will be broadcast exclusively on Netflix. Is there a risk of overload? Certainly. But though the Universe has accumulated its critics (many of them against the departure of Edgar Wright from his Ant-Man dream project), it's here to stay, and its formula is being imitated by both DC Comics (who are rushing Batman and Wonder Woman into the next Superman film) and Sony (who are making a Sinister Six film focused on Spider-Man villains). Naturally, the films that make up the Universe have provided employment for many actors, many of whom have launched or revived their careers on the back of its success. The following thirteen individuals have also made appearances, though you'd be forgiven for failing to notice them given the star power and memorable supporting turns and cameos (from Stan Lee's obligatory appearances to Chris O'Dowd's awkward date with Natalie Portman and Harry Dean Stanton's provision of a pair of pants to the Hulk) that they share the screen with. For articles similar to this, please see 24 People You Didn't Know Were In 24, 23 People You Didn't Know Were In A Bond Film or 20 People You Didn't Know Were In A Harry Potter film. Let's begin, shall we?