Tonight marks a major milestone for Law & Order: SVU, as the popular spinoff airs its 400th episode. Like the original Law & Order series, SVU has managed to land a number of A-list stars during its near-20-year run—including well-promoted guest turns by the likes of Robin Williams, Alec Baldwin, and Whoopi Goldberg (not to mention a cameo by former VP Joe Biden last September). But—again, much like the original seriesSVU has also served as a proving ground for hundreds of talented newcomers looking to build their resumes, including a handful of future Oscar nominees, like these five. These are their stories.

1. MICHAEL SHANNON

Later this month, Michael Shannon will compete for a Best Supporting Actor Oscar for his role as a rough-and-tumble Texas detective in Tom Ford’s Nocturnal Animals. It’s not the first time Shannon has been an Oscar nominee; he earned a nod in the same category in 2009, for Sam Mendes’s Revolutionary Road. But four years before that, Shannon appeared in "Quarry," a season six episode in which he played an abuse victim-turned-murder suspect.

2. MAHERSHALA ALI

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Among Michael Shannon’s competition in this year’s Best Supporting Actor race is Moonlight’s Mahershala Ali, who appeared in "Unstable," a 2011 episode of SVU. Ali played a former Wall Street trader who becomes the prime suspect in a series of rapes and murders, but the truth is not so straightforward.

3. ROONEY MARA

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Though she’s just 31 years old, Rooney Mara has already been nominated for two Oscars: first in 2012, for Best Actress in David Fincher’s The Girl With the Dragon Tattoo, then again last year, for Best Supporting Actress in Todd Haynes’s Carol. But more than a decade before all that, she played a formerly overweight teen who bullies overweight teens in the 2006 SVU episode "Fat." She caused a bit of a PR stir in 2011 when she told Allure that the episode "was so awful." Fans of the series were none too happy with the actress, who promptly set the record straight, clarifying that, "If anything, I didn't mean that the storyline was ridiculous; I meant that humanity is ridiculous."

4. BRADLEY COOPER

Though he’d already had major roles on short-lived series like The $treet, Touching Evil, and Jack & Bobby (as well as a multi-season arc on Alias), four-time Oscar nominee Bradley Cooper was far from a household name in 2005. That’s when he played sleazy lawyer Jason Whitaker in the season six episode, "Night."

5. AMY RYAN

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Like Bradley Cooper, Amy Ryan had also appeared in a couple of quickly canceled series—I’ll Fly Away and The Naked Truth—when she appeared on SVU in 2000’s "Bad Blood" episode, in which a murder at a party leads Benson and Stabler to a dysfunctional family. Three years later, she became a major character on The Wire. In 2008, the same year she began playing Holly Flax on The Office, she earned a Best Supporting Actress nomination for Gone Baby Gone. (An even bigger prize came later, when Holly married Steve Carell’s Michael Scott on The Office.)