It's become a trend for Hollywood's summer blockbusters in recent years: cast a little-known actor in a prominent role. Why cast big-name actors when you can throw the millions you save on salaries into special effects, right? Summer is usually the playground for escapism at the theater anyway.
The movies with little-to-no plot sell millions and millions of tickets, and actors go from largely unknown to household name.

It happened in 2007 when Megan Fox took on the role of Mikaela Banes in Michael Bay's "Transformers." It happened again in the summer of 2009 when Chris Pine stepped into the shoes of James T. Kirk in J.J. Abrams' "Star Trek."

It will happen again this summer when several unknowns take on the biggest role of their career and suddenly move from the C-list to A-list celebrity. Here are five actors you might not know now, but will know before the summer is over.

Up First: The Mighty Thor

Chris Hemsworth

The summer's first superhero movie, "Thor" (coming May 6), features Chris Hemsworth as the god of thunder in this adaptation from Marvel Comics.

Hemsworth will reprise the role in superhero supergroup movie "The Avengers," which is currently filming, but his most recognizable film role to date was as George Kirk, James Kirk's father, in J.J. Abrams' "Star Trek" reboot.

Prior to that, the Australian-born actor only had TV roles to his credit, the biggest of which came on the Australian soap opera "Home and Away."

You'll get to see more of Hemsworth later this year in the horror flick "Cabin In the Woods" and the remake of "Red Dawn," where he'll take on the role of Jed Eckert, played by Patrick Swayze in the original.

Up Next: Dakota's Little Sister

Elle Fanning

She's mostly known as Dakota Fanning's younger sister, but that will change with two major projects on the horizon.

Elle Fanning will appear in "Super 8" (June 10), the sci-fi film written and directed by J.J. Abrams and produced by Steven Spielberg.

Although she's been acting since 2001, Elle's early career featured mostly bit parts and scenes playing a younger version of her sister. Her first independent role came in the 2003 Eddie Murphy bomb "Daddy Day Care." She followed that with prominent roles in the 2004 film "A Door In the Floor," starring Jeff Bridges and Kim Basinger, and 2007's "Reservation Road," starring Joaquin Phoenix and Jennifer Connelly.

Later this year, Elle will appear in "We Bought a Zoo," directed by Cameron Crowe ("Almost Famous") and starring Matt Damon and Scarlett Johansson.

Up Next: Megan Fox's Replacement

Rosie Huntington-Whiteley

She's never done any acting, but Rosie Huntington-Whiteley will get a prime spot battling giant robots alongside Shia LeBeouf in the third installment of the Transformers franchise, "Transformers: Dark of the Moon," hitting theaters July 1.

Huntington-Whiteley's character, Carly, replaces Megan Fox's Mikaela Banes as the female lead in the final film in the Transformers trilogy.

Fox played Banes in the first two Transformers films, "Transformers" and "Transformers: Rise of the Fallen," but was dropped from the third after referring to director Michael Bay as Hitler and Napoleon during an interview.

Bad news for her, good news for Huntington-Whiteley, who is most widely known as a Victoria's Secret model. She met Bay while he was filming a commercial for the lingerie giant.

Up Next: The First Avenger

Chris Evans

You probably don't recognize the name, but 29-year-old Chris Evans has already appeared in 18 movies, more than a few that you've likely already seen.

His credits include the slapstick comedy "Not Another Teen Movie," Danny Boyle's sci-fi gem "Sunshine" and both "Fantastic Four" movies, in which he played the ever-cocky Human Torch, Johnny Storm.

If you look at Evans' roles, you quickly realize he's normally part of an ensemble cast. Well, no more! Evans will get plenty of screen time this summer while tackling his biggest role to date in "Captain America: The First Avenger," which debuts July 22.

He'll also play the same role in "The Avengers," set to be released in 2012. Taking on one of Marvel Comics' most iconic heroes should transform Evans' from that guy who played Johnny Storm to household name.

Last Up: A New Barbarian

Jason Momoa

You've probably never heard the name Jason Momoa, but you'll know it by the time summer is over. The Hawaiian-born actor is stepping into a really big pair of shoes -- those of Arnold Schwarzenegger.

Momoa will star as Conan in a remake of the film that transformed Schwarzenegger from the bodybuilder with the funny accent to action star, "Conan the Barbarian" (Aug. 19).

While it will be Momoa's first starring role in a major motion picture, he's somewhat familiar with action/adventure territory. Momoa cut his teeth in the genre playing Ronon Dex on the Syfy series "Stargate: Atlantis" from 2005-2008 and more recently played Khal Drogo on HBO's "Game of Thrones."

He's also had runs on some much lighter fare -- "Baywatch" and the short-lived Fox prime-time soap "North Shore" -- but that will likely be all behind him following his breakout summer.