How well do you remember guest stars on "ER"?

One of the rare instances of a gifted child actor transitioning into a successful adult actor, Kirsten Dunst was already well-known for her roles in "Interview with the Vampire," "Little Women," and "Jumanji" before appearing as a homeless teen, Charlie Chiemingo, in "1996." Since then, she's acted in the "Spiderman" trilogy, "Elizabethtown," and "Melancholia."

Nearly a decade prior to starting her Primetime Emmy Award-winning role as Claire Dunphy on "Modern Family," Julie Bowen had a recurring role as Roxanne Please, an insurance saleswoman whose relationship with Carter eventually ended due to their busy schedules and his growing feelings for a med student, Lucy Knight. Audiences at the time may have recognized Bowen as Virginia Venit in "Happy Gilmore."

By the time he played ailing med student Paul Nathan, Cheadle was already well known for his TV roles on "The Golden Palace" and "Picket Fences." He'd also already racked up cinematic fame for his parts in "Boogie Nights," "Traffic," and "Swordfish." Since then, Cheadle has joined the Marvel Avengers, published a book about the genocide in Darfur, created a charity poker tournament, been named a UN Goodwill Ambassador, and received a number of awards for his humanitarian efforts in the Third World.

In one of the saddest story arcs ER ever produced, Lucy and Carter were stabbed by Paul Sobriki, a schizophrenic patient in the midst of a psychotic break. The stabbing led to Carter having issues with his kidneys and drug addiction, but some would say he fared better than Lucy, who died of a pulmonary embolism, despite attempts to save her. In reality, Kellie Martin had asked to be written off the show for personal reasons. Her sister had died of lupus and she found it too difficult to act in a medical setting.

Critically acclaimed actor David Krumholtz brought depth and passion to the role of the troubled Paul Sobriki, who stabbed Carter and Lucy because he thought they were trying to steal his internal organs. Krumholtz was known on the big screen for his roles in "The Santa Clause," "Addams Family Values," and "10 Things I Hate About You." Five years after his spot on ER, he was cast as math genius Charlie Epps on the crime drama, "Numb3rs."

Omar Epps played surgical intern Dennis Gant, who was constantly berated by Dr. Benton. At the end of season 3 episode,"Night Shift," a John Doe was brought into the ER after being hit by an el-train. Some witnesses said the man jumped, others said he fell. The staff page Gant to come assess the patient, and when the patient's beeper goes off, the staff realize the unrecognizable John Doe on the table is Dennis Gant. Epps' luck with bad hospital bosses didn't end when he became Dr. Eric Foreman on "House," but at least Foreman was able to stand up to his insensitive boss.

In season 12, Ray slept with Zoe (a then relatively unknown Kat Dennings), whom he met at a bar. He later broke up with her after finding out that Zoe was underage when she showed up at the ER to be treated for chlamydia. She later returned to Ray, seeking escape from her abusive father. Ray beat up the father while helping her escape. Dennings went on to play Darcy Lewis in the "Thor" films and Max on "2 Broke Girls."

Hargitay played the unreliable and overly emotional Cynthia Hooper a year before being cast in "Law & Order: SVU" for its first season. Cynthia is best remembered for her relationship with Mark Greene. She traveled to California to support him when his mother fell ill, despite not having been invited. They broke up and Cynthia quit her job at County General to avoid Mark. Things worked out well for Hargitay, as she has now been playing Detective/Sergeant/Lieutenant Olivia Benson for 18 seasons and is still going strong.

In one of ER's most critically acclaimed and award-winning episodes, Bradley Whitford played Sean O'Brien, whose pregnant wife, Jodi, was misdiagnosed by Mark Greene and died at the end of the episode, leaving Sean to raise his newborn son alone. Sean later sued Dr. Green for wrongful death and malpractice. Four years later, Whitford joined the cast of "The West Wing" as John Lyman, and in 2017, played Dean Armitage in the horror film, "Get Out."

Piper Laurie appeared for two episodes in season 2 as Sarah Ross, the mother of Doug Ross (George Clooney). Besides her role on "Twin Peaks," Laurie was already well-known for her roles in "The Hustler," "The Thornbirds," and "Carrie."

Dr. Kim Legaspi was important to the world of "ER" as she was Dr. Kerry Weaver's first girlfriend and helped her to realize her sexuality. Kim was played by Elizabeth Mitchell, who was fresh in audience's minds from her role in the film, "Frequency," the same year. Since then, Mitchell has played Juliet on "Lost," Rachel on "Revolution," and Ingrid the Snow Queen on "Once Upon A Time."

The final season of "ER" was packed with guest stars, one of them was Sarandon as Nora. In the episode that revisits a few familiar faces, Sam and Neela fly to Seattle to get a heart for an organ transplant patient in Chicago where they encounter Doug Ross and Carol Hathaway, still together and still working in the medical field. When Carol finally convinces Nora to sign off on the transfer, the grandchild's kidney ends up being transplanted into another familiar face, Dr. John Carter.

Dr. James McNulty was played by the loveable and grumpy Ed Asner. Best known for his role as Mr. Grant on the "Mary Tyler Moore Show," Asner is also known as the voice of Carl Fredrickson in "Up" and Santa in "Elf."

Ewan McGregor, who played young Obi-Wan Kenobi in the "Star Wars" prequels, visited Chicago and robbed a convenience store while nurse Carol Hathaway was shopping. She tends to the injured hostages with what few supplies she can gather, such as a juice box straw and a pen to perform a tracheotomy. Two years away from appearing in the prequels, McGregor was already known to audiences as Renton in the cult classic, "Trainspotting."

Marilu Henner is known to older fans as Elaine from "Taxi" and Ava Evans Newton from "Evening Shade." Younger fans might know her as Vivian Ludley from "Brooklyn Nine-Nine." However, the staff of Chicago General knows her as Linda, the overbearing woman who is brought into the ER alongside her new daughter-in-law, both having been injured in a drunken brawl during the wedding reception. Linda spent most of her screen time forcing her son to choose between his mother and his wife.

Ray Liotta took center stage as Charlie Metcalf in the season 11 episode, "Time of Death." Whereas most episodes showed an overview of the treatment of multiple patients, Metcalf was the only patient in this episode, which also ran in real time (similar to 24). He faded in and out of consciousness, with bits of County General bleeding into his hallucinations. Watching the alcoholic Metcalf try to reconcile with his estranged son before he dies of cirrhosis inspired Pratt to reach out to his own alcoholic, absentee father.

Danny Glover may have been "too old for this" as Roger Murtaugh in the "Lethal Weapon" movies but didn't let age stand in the way of reconnecting with his on-screen son, County General's own Greg Pratt. In addition to roles in "Brothers & Sisters," "Dreamgirls," and "2012," Glover has received numerous awards for his humanitarian work and was given a UNICEF Ambassadorship.

The award-winning Ivy League actress, best known for her roles in "What’s Love Got To Do With It" and "How Stella Got Her Groove Back," took over as County General’s ER chief for the final season, along with her husband, played by her real-life spouse, Courtney B. Vance. Early episodes hinted at tensions due to a family tragedy. Eventually, it was revealed the couple had once had a young son who died in the County General ER under the care of Dr. Mark Greene, who reappeared in flashbacks.

Among the multitude of roles played by the prolific Stanley Tucci, audiences know him as Dr. Erskine from "Captain America," Caeser Flickerman from "The Hunger Games," and Nigel from "The Devil Wears Prada." His character on "ER" is mostly remembered for being a jerk to the staff and having a drunken one-night stand with Abby, which led Luka to deliver a well-deserved punch to the face.

Yep, Sid the Sloth went to medical school, as did Tybalt from Baz Luhrmann's "Romeo + Juliet" and Chi Chi from "To Wong Foo, Thanks For Everything Julie Newmar." The loveable comedian and actor, John Leguizamo, played the often antagonistic Dr. Victor Clemente, who in span of 12 episodes, managed to be a suspect in an attempted murder, got framed by his girlfriend's corrupt cop husband , suffered PTSD after being attacked by the aforementioned cop, and attacked a nearby taxi in his rage. It's no wonder County General decided he was a liability and axed him!

Alan Alda is better known for playing Hawkeye Pierce in M*A*S*H, as well as Arnold Vinick in the final seasons of "The West Wing." On ER, he played Dr. Gabriel (Gabe) Lawrence, a former teacher, and mentor of Chief Kerry Weaver, who brought him on board at County. It eventually became clear to both the audience and the hospital staff that Lawrence was showing signs of Alzheimer's. In real life, Alda is in full control of his mental faculties, serving as a visiting professor at Stony Brook University and on the boards and committees of several STEM foundations.

James Woods, known for his roles in "Shark," "The Way We Were," "Casino," and "Nixon" appeared in a flashback-heavy episode on "ER," where the audience saw him go from the energetic med school professor who jumped on desks and encouraged Abby not to drop out, to the wheelchair confined individual who had to communicate through an AI eye movement based interface.

Kristen Johnston played the unpopular and brash nurse in charge for six episodes, but is better known for her role as Sally Solomon in the sitcom, "Third Rock From the Sun." In 2012, Johnston published her autobiography in which she outlined her struggle with addiction.

Acclaimed actor James Cromwell earned an Emmy nomination for his role as Bishop Lionel Stewart on "ER." Stewart, dying of lupus, coaxes Luka to face the demons of his past and the truth of what happened to his family in Croatia. The audience learned that Luka refused the chance to evacuate during the Croation War of Independence because he wanted to finish his internship. This mistake came back to haunt him when his family's apartment building got hit by a mortal shell. His son died instantly, but he was forced to choose between his wife and his daughter. Luka confessed to Bishop Stewart that he could have saved his wife by carrying her to safety, but instead chose to give CPR to his mortally injured daughter. The CPR failed and both Luka's wife and daughter died. Bishop Stewart granted Luka absolution for the death of his wife and reminded him that it was an impossible choice. With this, Luka finally began to heal.

Bob Newhart has delighted audiences for decades with his stammering delivery and deadpan wit. He starred in not one, but two hit sitcoms during the 1970s ("The Bob Newhart Show" and "Newhart"). He also played Santa in the modern holiday classic, "Elf." Newhart, who has won Emmys, Grammys, Golden Globes, and Peabody Awards for his TV shows, is still going strong.

Legendary actor Forest Whitaker has been acting since 1982, taking on dramatic roles like Big Harold in "Platoon," Jody in "The Crying Game," Idi Amin in "The Last King of Scotland," and more recently, Saw Gerrera in "Rogue One: A Star Wars Story." Over the course of his six-episode arc on "ER," he played Curtis Ames, a carpenter initially treated by Kovac for pneumonia and then suffered a stroke. He blamed Kovac for the stroke, but when his attempt to sue the doctor failed, he resorted to stalking. The action culminated with Ames abducting Kovac and crushing the doctor's hand in a vice before shooting himself in the head for Luka to witness.

Armand Assante, known for playing Mafia bosses in films like "Gotti" and "Hoffa," appeared in four episodes of "ER" as the wealthy Richard Elliot. Elliot was impressed by the thorough care he received from Sam in the ER, as well as her ability to anticipate his needs. He offered her a lucrative job as a part-time home nurse working for him, which she accepts after he says she can continue working full time at County General.

Peter Fonda, best known as Captain America/Wyatt in "Easy Rider," played Pierce Tanner in the 300th episode of "ER," aptly named "300 Patients." Tanner arrived in the ER to check on his wife, Melissa, who was in the car with Lowell, the now-adult son they gave up at birth because of his Down Syndrome. Tanner found out that Melissa had been visiting Lowell every week since his birth, without Pierce knowing. In real life, Peter Fonda is Bridget and Justin Fonda's father and stepfather to Thomas McGuane Jr. He is the son of Henry Fonda and the younger brother of Jane Fonda.

John Mahoney is probably best known for playing working-class, retired police officer Martin Crane on NBC's "Frasier," but his one-off appearance on "ER" as aging drag queen Bennett Cray earned praise for both his acting and his singing. Most people would be surprised to learn that the all-American-sounding Mahoney is actually from Blackpool, England.

Acting phenom and activist Sally Field played Maggie Wyczenski, who had a tumultuous relationship with her daughter, Abby. Over the course of the 12 episodes in which Maggie appeared, Abby and Maggie shared truths, healed wounds, and eventually, made peace after the birth of Abby's son, Joe. Sally Field has been on both small and big screens since the 1960s, from serious roles in "Norma Rae" and "Brothers & Sisters," to comedic characters in "Mrs. Doubtfire" and "Legally Blonde 2: Red, White, and Blonde."

For her 5-episode role as Eleanor Carter, Mary McDonnell earned a Primetime Emmy nomination. But it was her role as President Laura Roslin on "Battlestar Galactica" that made her recognizable to audiences worldwide. She also played the ultimately doomed First Lady Marilyn Whitmore in "Independence Day."

America's favorite 80's TV dad, Michael Gross, went from comedy to drama, when "Family Ties'" Steven Keaton became "ER's" Jack Carter. He later went back to comedy as Alfred Mosby on "How I Met Your Mother." Playing a character in "ER" was a nice treat for Gross, since he is a native of Chicago, the home of County General.

During his time in Africa, Carter met the half-Congolese/half-French, Kem, played by the half-Zimbabwean/half-English, Thandie Newton. Kem appeared in 14 episodes between 2003 and 2009. She is best known for her film roles in "Crash" and "Mission Impossible 2," and her TV roles in "Westworld" and "Rogue."

The death of Dr. Michael Gallant in Iraq led to an argument at his funeral between his widow, Neela, and his father, James, about the virtues of war. Col. James Gallant was played by Ernie Hudson, who played Warden Leo Glynn in the gritty HBO jail series, "Oz," and Winston Zeddmore in the first two "Ghostbusters" movies (and a cameo at the end of the 2016 remake).

The stern, but loving, David Greene was played by John Cullum, who earned an Emmy nomination for his role as Holling Vincoeur on "Northern Exposure." He was already acquainted with Anthony Edwards (Mark Greene), as Edwards had played the recurring role of Mike Monroe on "Northern Exposure." Cullum began his long career on Broadway in 1960's "Camelot" and has since appeared on TV shows, such as "Law & Order" and in movies, such as "The Conspirator."