Many patients (played by guest actors) visited the NBC medical drama
ER while the TV series was airing in the '90s and the '00s — and many of those actors went on to become household names. It's time for a ranking , because so many celebrities visited County General, and we didn't even know it back then. The list includes actors who would go on to star in ER guest stars Gilmore Girls, Breaking Bad, Gossip Girl, Mad Men, Saw and Wonder Woman. Not bad.
The hit medical drama premiered in 1994 and ran on NBC for 15 seasons until 2009. That's 331 episodes-worth of guest stars who visited the fictional hospital.
E.R.'s main original cast included George Clooney (who played Dr. Doug Ross), Anthony Edwards (who played Dr. Mark Greene), Noah Wyle (who played Dr. John Carter), and Julianna Margulies (who played Nurse Carol Hathaway). And the series went on to welcome many new medical professionals over the years, including Angela Bassett (Dr. Catherine Banfield), John Stamos (Dr. Tony Gates), Maura Tierney (Dr. Abby Lockhart), and Kellie Martin (Dr. Lucy Knight).
You may not have known it at the time, but many of the guest-starring patients those main characters treated would go on to become big names themselves. Here are the best guest stars from
E.R.'s long history, ranked from awesome to most awesome. 1 Matthew Settle
Attention, Upper East Siders: Before Settle played Rufus Humphrey on
Gossip Girl, he guest starred on as Abby's neighbor Brian, who is an abusive husband to Joyce (played by Christina Hendricks). ER in 2002 7 Shiri Appleby
UnREAL actor appeared in the 1994 pilot episode of ER as a pregnant teenager. Years later, Appleby would join the medical drama as intern Dr. Daria Wade in ER's final season in 2009.
Elle the following in 2015 about her two roles on ER: "I was in the pilot of I played a 15-year-old pregnant girl they were treating. And then in the final season they were casting for interns. I had literally just been in the actual E.R. because I broke my pelvis and tailbone and told my agent, 'I really want to be on ER, ' So then I was in the entire last season of the show. It was amazing. It was like being in graduate school for television. I learned that this is how you do television at the highest level." ER 11 Nick Offerman
Uudiences loved Offerman as
Parks & Recreation's Ron Swanson. Years previous, the actor guest-starred as rocker named Rog in the 1997 live episode of . ER 12 Adam Scott
Parks & Rec co-star also guest starred on ER. Scott played David Kerstetter in a 1995 episode from the show's first season.
Scott told TVLine the following about the role: "It was the
first season of , so it was a pretty big. Everyone was discovering it, and George Clooney was on the cover of ER TV Guide as this new star. I was sitting outside waiting to work and he was playing basketball with a bunch of dudes. I remember just thinking, ‘God, this dude is on the cover of TV Guide!'" 14 Eric Stonestreet
Modern Family actor guest starred in a Season 7 episode of ER as a Star Trek fan who attempted to Vulcan-ize his ears. 16 Josh Peck
One half of
Drake & Josh guest starred on a 2001 episode of . Peck played Nick, a teen who needs a third heart transplant. ER 19 Alexis Bledel
Gilmore Girls and Handmaid's Tale actor guest starred on the final episode of , playing Dr. Julia Wise, a new intern at County General. ER 20 Aaron Paul
Paul is known for his Emmy-winning role as Jesse Pinkman on
Breaking Bad. Years before the AMC drama premiered, the actor guest starred on as a very Jesse-like character named Doug. ER's ninth season 21 Tobin Bell
The doctors of County General were totally unaware that the future Jigsaw of the
Saw movies played a hospital administrator in . ER's 1994 pilot episode 22 Josh Hutcherson
ER Season 9, played Matt, a young boy whose family is killed by a drunk driver in a 2002 episode. The Hunger Games actor 23 David Schwimmer Paul Morigi/Getty Images Entertainment/Getty Images
Friends actor made an uncredited audio-only cameo in a 1996 episode of as Dr. Karubian, a surgeon called by Dr. Carter. ER 24 Mariska Hargitay Law & Order: SVU's Hargitay played ER front desk clerk Cynthia Hooper throughout . She and Dr. Greene have an imbalanced relationship that ends with him breaking up with her in California. ER's Season 4 in 1998 26 Shia LaBeouf
2000 episode of , LaBeouf played Darnel Smith, a smart-mouthed young man in a wheelchair who has muscular dystrophy. ER 27 Anton Yelchin
Star Trek actor appeared on ER at nine years old in a Season 6 episode that aired in 2000. Yelchin played Robbie Edelstein, a young boy whose parents both die in a car accident. 28 Ewan McGregor
Trainspotting actor guest starred as Duncan Stewart, who holds a group of people hostage (including Carol) during a convenience store robbery in Season 3.
In August 2017,
McGregor remembered the in an interview with ER episode The Hollywood Reporter: "I loved making it, and I loved working with Julianna Margulies a lot because I was a big fan of that show, and I asked to be on it. I told my agent to see if I could be on it because I was a big fan. And I loved her. I love her work. So I remember I mainly worked with her, and it was like a special one hour. It was all shot in Chicago. I enjoyed it." ER 33 Bradley Whitford
Before giving us chills in
Get Out, Whitford played Sean, a young dad-to-be accompanying his pregnant wife to the hospital in a devastating Season 1 episode. 34 Dakota Fanning
Ocean's 8 actor's first big role was playing Delia Chadsey, a young girl who is taken to the ER after a car accident and finds out her leukemia has returned. Fanning was just 6 years old at the time. 35 Eva Mendes
Get this —
Mendes' very first IMDb credit is her guest-starring role on ER in 1998. The actor plays a concerned babysitter named Donna, who brings in a young girl she was caring for. 36 JK Simmons
The Oscar-winning actor guest starred on
. Simmons played Gus Loomer, a man who is involved in a fatal car wreck. ER Season 10 in 2004 37 Jessica Chastain
The Oscar-nominated actor appeared in
ER Season 10 in 2004, in which she plays a daughter accompanying her father to County General. It is Chastain's first acting credit, according to IMDb. 38 Octavia Spencer
The Oscar-winning actor once made an
appearance on an , in which she played a woman named Maria who fake pains in order to find out if she was pregnant with a boy or a girl. ER Season 5 episode 39 Zac Efron
Yup, you read that right. Efron rolled up to the doors of County General in a
2003 episode as Bobby Neville, a young man with a fatal gunshot wound. 40 Chris Pine
Wonder Woman actor got his first credited role as a guest star on the NBC medical drama. In a 2003 episode, Pine played Levine, who visits the ER after drinking too much at a Valentine's Day party. This is Pine's first IMDb credit, according to an IMDb interview with the actor. "I remember on the stage they built and the entire ER was unbelievable," he told IMDb in the video interview. "It was my first time doing anything scripted and long, and it was really neat."
Can you believe so many amazing actors visited
ER as patients and guest stars? It'll make you want to revisit the series and pay some more attention to the guest cast that comes through.