10 Celebs You Forgot Guest Starred On 'Law And Order: SVU'

With the show being renewed for a record-breaking 21st season, we take a look back at some of the series' most famous guest appearances.

Upon its renewal, the popular crime drama has now officially become TV’s longest-running primetime live-action series, surpassing the 20 seasons set by mothership series Law & Order, and Gunsmoke.

Mariska Hargitay, who plays Olivia Benson in the show, said in an interview with Today:  "I'm deeply proud to be a part of this groundbreaking show, and humbled to make television history today."

"The longevity and continued success of SVU is a testament not only to the show's powerful storytelling and ability to connect with viewers, but to its necessity," she added. "We have told important stories for 20 years, and we will continue to tell them."

To celebrate the major milestone, we're taking a look at some of SVU's guest appearances -- and you may be surprised at some of the big names.

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Serena Williams- "Brotherhood" (Season 5, Episode 12)

Image: NBC

In one of her first-ever acting roles, the tennis star took on the role of Chloe Spiers in the season five episode, "Brotherhood." Playing a victim of revenge porn, her story leads detectives to discover the seedy underbelly inside a college fraternity.

Kathy Griffin -  "P.C." (Season 11, Episode 13)

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The comedian played Babs Duffy, a lesbian activist who is furious the NYPD wasn't taking enough action following a spate of assaults and rapes against lesbians. During the investigation, LesBeStrong spokeswoman Babs tries to make a move on Olivia Benson, who shuts down the attempted kiss.

Robin Williams - "Authority" ‎(Season 9, Episode 17)

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The late actor starred in the 200th episode of the series, portraying an engineer who makes prank phone calls to SVU officials and kidnaps Detective Olivia Benson (Hargitay). His performance was so convincing, that he was nominated for an Emmy for the role.

Amanda Seyfried - "Outcry" (Season 6, Episode 5)

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The same year she made her film debut in the iconic flick Mean Girls, Amanda Seyfried starred as Tandi McCain, a high school student who claimed she was raped by construction workers but changed her version of events during the investigation and trial.

Sarah Hyland - "Suppression" (Season 3, Episode 1) and "Hothouse" (Season 10, Episode 12)

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Sarah Hyland has actually made two appearances on SVU -- in 2001 and 2009. For her first guest spot, she played the daughter of a suspected child abuser named Lily Ramsey in an episode titled "Suppression". In 2009, in great contrast to her role as the vapid Hayley Dunphy in Modern Family, Hyland starred as the incredibly brainy Jennifer Banks, who suffered from a psychotic breakdown over the pressure of her studies and murdered her roommate.

Hilary Duff - "Selfish" (Season 10, Episode 19)

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Singer and Lizzie McGuire star Hilary Duff starred as Ashlee Walker, a young mum whose daughter dies of measles after being exposed by an unvaccinated child.

Bradley Cooper - "Night" (Season 6, Episode 20)

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Way back in 2005 the A Star Is Born actor played a character named Jason Whitaker on two SVU episodes. His first appearance was in an episode of franchise spin-off, Law & Order: Trial by Jury, and the second episode was on SVU. In both episodes, he plays a lawyer suspected of murder.

Luke Perry - "Trials" (Season 10, Episode 1)

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Before starring as Fred Andrews on Riverdale, the late Luke Perry appeared in SVU's tenth season as a serial rapist who marries one of his victims. His Riverdale co-stars Lili Reinhart, Casey Cott, Skeet Ulrich, and Marisol Nichols have also made guest appearances on the show before finding fame with the popular series based on Archie comics. Perry died from a stroke last month aged just 52.

Norman Reedus - "Influence" (Season 7, Episode 22)

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Before he slayed zombies on The Walking Dead, Norman Reedus starred in a 2006 episode of SVU as Derek Lord, a former rock star who encourages a fan, Jamie Hoskins (Brittany Snow), to go off her bipolar medication.

Whoopi Goldberg - "Institutional Fail" (Season 17, Episode 4)

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Whoopi appeared in the series as overworked casework supervisor Janette Grayson, who was investigated by the Special Victims Unit after a young girl named Keisha is found locked in a dog kennel, beaten and starved. She later dies due to her injuries. Police later find out that Grayson had pressured social workers in charge of Keisha to falsify visit reports, and had not checked on the young girl for several months prior to her death.

Image: NBC