Does the world really need another Olsen sister? Up until last weekend, we're fairly certain that most movie-goers would have responded to that question with a resounding "no."

But then Sundance audiences got a chance to see Elizabeth Olsen in her pair of harrowing breakout performances in the indies 'Martha Marcy May Marlene' and 'Silent House.' Faster than you can say "John Stamos," Mary-Kate and Ashley's younger sibling has become the talk of two towns -- Park City, Utah, and Hollywood, Calif.

But who is this blushing young ingenue, a girl whose only screen credits prior to 2011 consisted of cameo roles in her overachieving sisters' direct-to-video and TV movies? Join us after the jump for all you need to know about the Sundance Film Festival's latest rising star.
Like Sundance's other "it girls" of recent memory -- Carey Mulligan (from 'An Education') and Jennifer Lawrence ('Winter's Bone') -- the 21-year-old Olsen has star potential written all over her.

Tasked with the burden of being the focal point of not one, but two tense, psychological thrillers debuting at the festival, Olsen has been garnering rave reviews for her portrayals of troubled young women. 'Silent House' concerns a girl trapped in a seemingly haunted summer house, and it calls for Olsen to be on screen for almost the entirety of the film's 86 minutes, steadily ramping up the anxiety into hysteria in what is being marketed as movie filmed in a single, continuous shot in the vein of Hitchcock's 'Rope'. (Read our review of 'Silent House.')

'Martha Marcy May Marlene' is a different animal entirely, a far meatier role than a simple spookfest, and one that is already earning Olsen critical praise and national attention. In it, she plays the multi-named title character, an emotionally damaged escapee from a cult who seeks refuge from the ordeal with her sister, but who finds herself unable to truly distance herself from the past.

'Martha Marcy May Marlene Cast Interview

Are you shocked to discover that a member of the often-lambasted Olsen clan could prove to be such a compelling actress? Don't feel bad -- our reviewer, Jenni Miller felt the same, noting:

"It's both unfair and impossible to avoid mentioning Olsen's siblings are Mary-Kate and Ashley, if only to give context. There's a sort of gross and guilty undercurrent of surprise that, not only do they have another sister, but that she's an actress, and a very talented one to boot. In fact, that was pretty much my reaction, and it's not something I'm particularly proud of, though I'm no less delighted to have another whip-smart starlet on the horizon."

But the reason we haven't heard about Olsen is by the actress' own design, as you'll discover through our list of Need to Know Facts about Elizabeth Olsen:

Mary-Kate and Ashley Olsen1. All in the Family
Although Elizabeth got her first taste of showbiz through Mary-Kate and Ashley's burgeoning media empire in the '90s, the younger Olsen deliberately avoided following in her older siblings' dainty footsteps -- choosing to pursue theater training and acting classes instead of immediately launching into movies.

"I was very nervous to actually work," Olsen told THR. "I think that's why I focused so much on theater. I thought theater was a safer place because it's more free of media ... being in front of a camera was really the most frightening thing."

Still, Olsen was quick to assure 'The New York Times' that she wasn't purposefully trying to blaze her own trail -- her decision not to go the child-acting route like her sisters was more because of her own comfort level. "It wasn't intentional to be like, I don't want to go this route," she said. "They're two years older than me, but they feel much older than 24. They've been running businesses for a very long time."

When The Wrap asked why it seemed that her sisters hadn't helped Olsen break into the movie industry, she admitted that it was because she hadn't asked them to. "If I asked them they would have," she said. "But I wanted to do it without asking for the favor." We like her already.

Elizabeth Olsen2.She's not just a pretty face
Her looks seem like an odd amalgamation of her sisters and Maggie Gyllenhaal spliced with Ellen Page, but Olsen isn't about to coast by on what's on the outside; she's currently enrolled at the prestigious Tisch School of Arts at NYU, studying theater and psychology. Her fascination with the human mind is part of what attracted her to the twisted role in 'Martha Marcy May Marlene', according to Us Weekly.

She also spent a semester abroad in Russia to study acting at Moscow's Art Theatre School, has understudied in a number of on and off-Broadway plays, and enjoyed ballet and sports in high school. Oh, and she starred in a 2007 music video for alternative rock band Carlotta. Overachieving clearly runs in her family.

Elizabeth Olsen3. She has already proven to be more than a one-hit wonder
Most actors are lucky to even have one break-out hit at Sundance, let alone two, but Olsen didn't stop there. 'Martha' was her first screen role since 1995 (in her sisters' dubiously titled 'The Adventures of Mary-Kate & Ashley: The Case of the Mystery Cruise') but Olsen went for the hat trick, filming 'Martha,' 'Silent House' and another movie, 'Peace, Love and Misunderstanding' in quick succession. Starring Jeffrey Dean Morgan, Catherine Keener, Chace Crawford and Jane Fonda, 'Peace' sees Olsen's character taking a road trip with her brother and conservative mother to meet her estranged hippie grandmother.

During Sundance, it was announced that Olsen already had another high-profile project lined up: 'Red Lights,' co-starring Robert De Niro, Sigourney Weaver and Cillian Murphy. Olsen will play a psychology student (art imitating life?) assisting her professor (Weaver) in trying to debunk a world-renowned psychic (De Niro), while Murphy will play her boyfriend.

Time will tell if Olsen will see the kind of success that Carey Mulligan and Jennifer Lawrence have enjoyed since their breakthrough performances at Sundance -- or indeed the success of her sisters, who were practically self-made millionaires before they could even buy beer -- but judging by the buzz coming out of the festival this week, we think she's off to a great start.

Do you plan to see 'Silent House' or 'Martha Marcy May Marlene' now that they've landed distributors? Were you surprised to hear about the mysterious younger Olsen sibling? Share your thoughts below.

Follow Laura on Twitter@LauinLA.

Martha Marcy May Marlene
Based on 38 critics

A woman (Elizabeth Olsen) struggles to reintegrate into society after fleeing from a cult. Read More