Celebrities You Forgot Starred On Grey's Anatomy

Plenty of stars have been made through "Grey's Anatomy," including Katherine Heigl and Ellen Pompeo, whereas other stars, like Patrick Dempsey, were already quite famous by the time they joined the cast of the legendarily long-running medical drama. The series, which began in 2005 as a modest mid-season replacement created by Shonda Rhimes (now a legend in her own right), tells the story of a Seattle hospital that sees all sorts of unlikely and incredible medical cases ... which might not be particularly realistic but are plenty compelling all the same.

Aside from the core cast, many other actors passed through the halls of Seattle Grace Mercy West turned Grey Sloan Memorial Hospital over the years. And you might be surprised to learn about some of the incredibly famous faces who guest-starred on this beloved show. Here are just a few of the celebrities that you totally forgot showed up on "Grey's Anatomy."

Known for projects like "American Horror Story," "Run," and "Ratched," Sarah Paulson has become one of the most acclaimed performers in Hollywood, known for her all-consuming commitment to her roles and the way she's able to disappear into a huge variety of characters. However, long before finding widespread fame, Paulson popped up during a Season 6 episode of "Grey's" called "The Time Warp," playing one of the show's most influential doctors — Dr. Ellis Grey — in a flashback.

The mother of series lead Meredith Grey (Pompeo) and a trailblazing surgeon in her day — only to fall ill with early-onset Alzheimer's — Ellis is one of the show's biggest icons, so it makes sense that a performer like Paulson would play her. In a flashback relayed by Ellis' colleague and former love, Dr. Richard Webber (James Pickens Jr.), viewers watch as Ellis and Richard — who are secret lovers — try to help a patient with GRID, which is what medical professionals once called AIDS. There are several other flashbacks in the episode that don't feature the actress, but Paulson's presence elevates the entire hour.

Millie Bobby Brown might play a huge, pivotal role in a Season 11 episode of "Grey's," but amazingly, you don't even see her for most of the episode, which is a testament to Brown's sheer talent as a young actor. One of the breakout stars of Netflix's "Stranger Things," who's also appeared in original films on the streamer like "Enola Holmes," Brown is a phenomenal performer who manages to hold the audience's attention in the 2015 episode "I Feel the Earth Move."

After an earthquake strikes Seattle, several doctors get a frantic phone call from a young girl named Ruby (Brown), whose mother has just passed out and is having a serious medical emergency. As they try to find her location while coaching Ruby through helping her mom, Ruby's cell phone starts to die, making the situation that much more dire. Ruby eventually makes it to the hospital and saves her mother, but even off-screen, Brown's presence is unforgettable.

The doctors lose a lot of patients throughout "Grey's Anatomy," but luckily for Demi Lovato's Hayley May, resident surgeon Dr. Alex Karev (Justin Chambers) takes a huge leap to help her ... and ends up saving her life in the process. A Disney Channel star turned musician and actress, Lovato is known for everything from "Camp Rock" to "Eurovision Song Contest: The Story of Fire Saga," but hardcore "Grey's" fans remember them playing a seriously disturbed teenage girl threatening to take her own life.

Brought to the hospital by her concerned parents, Hayley is a wreck, screaming and threatening to harm herself — all while insisting that she's "not crazy." Karev manages to convince her not to hurt herself, telling her that he believes she isn't crazy, and though he's met with plenty of doubts from his colleagues, he turns out to be exactly right. As it turns out, Hayley has a bizarre disease where she can hear all of the functions happening in her body at all times, and living with it is making her seem completely insane. But once Karev figures out the treatment, Hayley is saved. "Grey's" has seen plenty of explosive guest turns, but Lovato's is unforgettable.

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Throughout the series, Richard Webber struggles with plenty of family issues, including his niece, Camille, who suffers from advanced ovarian cancer after being diagnosed at just 14 years old. Though she's later portrayed by Camille Winbush in Season 4, when viewers first meet Camille in Season 2, she's played by a super recognizable face: MCU star Tessa Thompson.

Thompson — who also appeared in shows like "Veronica Mars" around this time and eventually moved on to huge projects like "Creed," "Westworld," and "Thor: Ragnarok," — showed up in the two-part Season 2 finale, "Deterioration of the Fight or Flight Response" and "Losing My Religion," after Camille falls ill at her prom. To try to make it up to her, Richard demands that the hospital throw a prom that everybody in the hospital must attend. Though Thompson doesn't actually appear in a ton of scenes throughout the episodes, she definitely steals the spotlight every time she does.

After getting her start in films like "Signs" and "Little Miss Sunshine" — and earning an Oscar nomination in the process — Abigail Breslin would appear on "Grey's Anatomy" in 2006 before moving on to more adult projects like "Zombieland" and "Scream Queens."

In the early Season 3 episode "Sometimes a Fantasy," Breslin appears as Megan Clover, a strange girl with a bizarre history of injuries who's living with a foster family. Though Karev, who's tasked with caring for her, immediately suspects that her parents are abusive, Megan is quick to exonerate them, saying that they're the nicest parents she's ever had ... and that she has super powers. As it turns out, Megan has an insanely high tolerance for pain and is constantly challenging friends to injure her, leading to a sustained stomach injury. The whole plotline is pretty crazy, but Breslin, even at a young age, pulls the arc off with extreme ease.

You probably know singer, songwriter, and actor Leslie Odom Jr. from his Tony Award-winning turn as Aaron Burr in the original cast of "Hamilton" or his Oscar-nominated role as singer Sam Cooke in 2020's "One Night in Miami." But back in the day, he appeared on a vital episode of "Grey's Anatomy," right alongside actor Carl Lumbly (of "Alias" and "The Falcon and the Winter Soldier").

In Season 5's "There's No 'I' In Team," Odom Jr. appears alongside Lumbly and several other guest stars — including future "Scandal" regular George Newbern — as one of a dozen patients participating in a "domino surgery," where some patients donate kidneys and others in need receive them. Odom Jr.'s P.J. Walling is a pretty unwilling participant, due in large part to a difficult relationship with his father, Kurt (Lumbly). But when Kurt gets sicker even after he receives a kidney, P.J. must grapple with his dad's death. Odom Jr. is a dynamic, multi-talented performer, and his turn on "Grey's" just proves he's been amazing for years.

Fans of Ryan Murphy's high school acapella series "Glee" likely remember Matthew Morrison as the lovable, passionate teacher Will Schuester, which makes his turn on "Grey's" all the more chilling. Throughout the series, Dr. Jo Wilson (Camilla Luddington) slowly reveals tidbits about her past, including that she was homeless as a teenager and lived in her car, and finally, that she was once married to a man who abused her and knew her as Brooke. To escape him, she changed her name and ran away ... but eventually, Dr. Paul Stadler (Morrison) shows up in Seattle, hoping to get officially divorced so that he can marry another woman (who is another victim of his abuse).

Introduced in Season 13 when Jo's boyfriend Alex sees him at a convention, Morrison's Paul seems sweet at first, but when he returns for a two-episode arc in Season 14 — "1-800-799-7233" and "Personal Jesus" — viewers realize exactly why Jo ran away. Morrison usually sticks to cheerful musical theater projects, and his (doomed) performance as Paul is a frightening but enthralling change of pace for the actor.

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There's no argument amongst "Grey's" fans that Derek Shepherd is the love of Meredith Grey's life, but after he tragically dies in a car accident in Season 11, she realizes that she has to start dating again. After working with a patient who just so happens to be a matchmaker, Meredith reluctantly goes on a blind date, only to discover that the John she meets for lunch is actually meant to meet someone else. However, when Meredith and John — played by Josh Radnor — really hit it off, they ditch their dates entirely.

Of course, Radnor is best known for another role where he plays a man looking for love in all the wrong places — Ted Mosby, the problematic protagonist of "How I Met Your Mother." Though his "Grey's Anatomy" character seems, at first, like he could be a great match for Meredith, he ruins the date by telling her he finds single moms "desperate" (unaware that Meredith is a single mother of three). In classic Mosby fashion, John botches the date, and Meredith walks away, but Radnor's appearance feels like an amazing wink to fans of "Grey's" and "HIMYM" alike.