Rewind·Posted on Jan 28, 201826 Celebs That Prove Just About EVERYONE Has Been On "ER"Long before he was Ron Swanson, Nick Offerman was Rog.by by Christopher HudspethBuzzFeed Staff, by Crystal RoBuzzFeed StaffFacebookPinterestTwitterMailLink 1. Zac Efron NBC Episode: Season 10, Episode 3, "Dear Abby"Role: Before his singing, dancing, High School Musical days, Efron played Bobby Neville, a young boy suffering from a gunshot wound. 2. Ariel Winter NBC Episode: Season 15, Episode 15, "The Family Man" through Episode 21, "I Feel Good"Role: Before making her mark as Alex Dunphy on Modern Family, Winter had a several-episode arc on ER as a girl named Lucy whose mother has to undergo emergency transplant surgery after they crashed into an ambulance. 3. Shia LaBeouf NBC Episode: Season 6, Episode 12, "Abby Road"Role: Young, pre-Even Stevens Shia played Darnel Smith, a child suffering from muscular dystrophy, and his performance is a real tearjerker. 4. Eva Mendes NBC Episode: Season 3, Episode 15, "Exodus"Role: Ages before starring in films like Training Day, Hitch, and The Place Beyond the Pines (and also before making a baby with Ryan Gosling), Mendes played a good-hearted babysitter to a little girl with an E.coli infection. 5. Josh Radnor NBC Episode: Season 9, Episode 17: "The Advocate"Role: The future How I Met Your Mother star played a man name Keith, who was in the ER, being treated for an allergic reaction to penicillin. 6. Chris Pine NBC Episode: Season 9, Episode 16, "A Thousand Cranes"Role: Before his role as captain of the USS Enterprise, Pine had a small role as Levine, a drunk dude who visits the emergency room. 7. Rooney Mara NBC Episode: Season 15, Episode 19, "Old Times" and Episode 21, "I Feel Good"Role: Before starring in The Girl with the Dragon Tattoo and other major films, Mara had a small part on ER as Megan, a young mother who struggles with giving up her baby. 8. Gabrielle Union NBC Episode: Season 6, Episode 10: "Family Matters"Role: Before she became Mary Jane, Union played a high school student named Tamara Davis who drove into a telephone pole. 9. Chadwick Boseman NBC Episode: Season 15, Episode 6, "Oh, Brother"Role: Long before saving the world with his fellow Avengers as Black Panther, Boseman played Derek, a boxer who has to make a trip to the emergency room after a rough fight. And fun fact: his father is played in this episode by actor Carl Weathers, who famously played boxer Apollo Creed in the Rocky movies! 10. Lucy Liu NBC Episode: Season 2, Episode 3, "Do One, Teach One, Kill One"Role: A few years before making her mark as Ling Woo on Ally McBeal (and later on as one of Charlie's Angels), Liu played the mother of a 4-year-old boy with AIDS. 11. Ewan McGregor NBC Episode: Season 3, Episode 15, "The Long Way Around"Role: Not long after his breakout role in Trainspotting, McGregor played a shaggy-haired liquor store robber. 12. Josh Hutcherson NBC Episode: Season 9, Episode 8: First SnowfallRole: Long before running around with Katniss in the Hunger Games franchise, Hutcherson played Matt, a young boy who was run over by a drunk driver while building a snowman. 13. Adam Scott NBC Episode: Season 1, Episode 20, "Full Moon, Saturday Night"Role: Over a decade before he was making everyone laugh as Ben on Parks and Recreation (and a lot of other great stuff), Scott played a patient named David who had been hit by a car and suffered a super bad gash on his chest. 14. Kirsten Dunst NBC Episode: Season 3, Episode 5, "Ghosts" plus five more episodes sprinkled through Episode 22, "One More for the Road"Role: Okay, to be fair, Dunst had already made her mark as a child actor in films like Interview with the Vampire and Little Women prior to her stint on ER, but she played a homeless teen named Charlie who strikes up a friendship with Dr. Ross (George Clooney) and was still years away from starring in the O.G. Spider-Man film franchise. 15. Nick Offerman NBC Episode: Season 4, Episode 1, "Ambush"Role: Over a decade before he played Ron Swanson on Parks and Rec, Offerman played a guy named Rog whose bandmate, and "best damn bass-player" he knows, Boz is rushed into the emergency room. 16. Kat Dennings NBC Episode: Season 12, Episode 5, "Wake Up" through Episode 12, "Split Decision"Role: Before some of her bigger roles in The House Bunny, Nick and Norah's Infinite Playlist, and 2 Broke Girls, Dennings played Zoe Butler, a girl who hooks up with Dr. Barnett (Shane West) and reveals that she's actually 14 years old. 17. Kristin Davis NBC Episode: Season 1, Episode 13, "Luck of the Draw"Role: Before her days drinking cosmos and wearing Jimmy Choos on Sex and the City, Davis played a woman who accompanies her niece to the ER because of a hamster bite — and, of course, she hits on George Clooney. Because, duh, George Clooney. 18. Tobin Bell NBC Episode: Season 1, Episode 2, "Day One"Role: About a decade before traumatizing victims as Jigsaw in the Saw movie franchise, Bell threw his weight around as a hospital administrator at Country General. 19. Cara Buono NBC Episode: Season 15, Episode 22, "And in the End"Role: Way before playing Mike and Nancy's mom on Stranger Things, Buono got to play a brand new mom in the series finale of ER. 20. John Hawkes NBC Episode: Season 4, Episode 1, "Ambush"Role: Loooong before his turn as an Academy Award-nominated movie star, Hawkes played a production assistant helping film a documentary at Country General. 21. Deborah Ann Woll NBC Episode: Season 14, Episode 14, "Owner of a Broken Heart"Role: Before sinking her teeth into the role of Jessica on True Blood, Woll played a young nurse named Aurora Quill. 22. Stana Katic NBC Episode: Season 12, Episode 4: "Blame it on the Rain" and Episode 5, "Wake Up"Role: You may know her best as the co-star of Castle, but before then Katic played a patient who was in a coma for several years, but then suddenly woke up in the emergency room. 23. Michael Cudlitz NBC Episode: Season 2, Episode 16: "The Healers"Role: Long before portraying Abraham on The Walking Dead, Cudlitz played an injured fireman in a 1996 episode of ER. 24. Eric Stonestreet NBC Episode: Season 7, Episode 3Role: Another eventual Modern Family star, Stonestreet played a patient named Willie, who found himself in the ER after slicing up his ears, trying to make them look like Spock from Star Trek. 25. Josh Peck NBC Episode: Season 7, Episode 13: "Thy Will Be Done"Role: Before he became Josh, of Drake & Josh fame, Peck played a teen named Nick, visiting the ER in need of a heart transplant. 26. Aaron Paul NBC Episode: Season 9, Episode 12: "A Saint in the City"Role: Breaking Bad's Jesse Pinkman played Doug, an edgy teen who is responsible for taking care of his younger siblings after his mother falls ill.