From Evan Peters to Amber Heard, Here Are Some of the Biggest Stars to Appear on "Criminal Minds"

Lynch had a recurring role on "Criminal Minds," playing Spencer Reid's (Gubler) mother, Diana Reid. The Emmy-winning actor and comedian first appeared on the show in the season one finale episode, with the season 15 finale marking her last appearance as Diana.

The late actor made an appearance in season four of "Criminal Minds" in episode three, titled "Minimal Loss." The "Beverly Hills, 90210" star played a cult leader named Benjamin Cyrus, who has the BAU on his tail for disturbing cases of statutory rape.

The veteran actor, who most recently played Victor Creel in "Stranger Things" season four, portrayed Detective Gassner, who helps the BAU solve a string of ceremonial murders in episode 19, "Heathridge Manor," during the seventh season of the police procedural drama.

Best known for his portrayal of Luke Skywalker in the universally beloved Star Wars franchise, Hamill played a serial killer, John Curtis, dubbed "The Replicator." Though his character is present throughout the season eight plot line, he appeared only in the final two episodes — "Brothers Hotchner" and "The Replicator." The actor told BuzzFeed in a 2013 interview how his daughter's love for the show translated into his role on "Criminal Minds": "Usually you don't have an arc like this where they set up something over a period of many, many episodes. As soon as I started watching these episodes, I said, 'Oh, I gotta do this!'"

In season one's episode 18, "Somebody's Watching," Heard — then an up-and-coming actor – played a Hollywood starlet named Lila Archer with a murderous admirer on the loose. Lila even explores a fleeting love interest with the series's lead, Spencer.

During the 10th episode of season one, "The Popular Kids," Paul played Mike Zizzo, the founder of a Satanic teenage group called the "Lords of Destruction," who is on the BAU's radar as a suspect in a string of murders. His guest appearance was long before Paul would portray his career-defining role of Jesse Pinkman on the acclaimed drama "Breaking Bad."

The Golden Globe-winning actor appeared on the show in a brief role of Fitz, the US embassy's regional security officer stationed in Barbados. In season 10, episode 19, titled "Beyond Borders," Brown's Fitz helps the BAU with their ongoing investigation of a missing family of four while on vacation. While Brown's screen time may have been short, this episode, in particular, served as a core premise of its spinoff "Criminal Minds: Beyond Borders," which ran for two years before getting canceled by CBS in 2017.

The "Firefly" and "Suits" actor stepped into the role of Detective Thea Salinas in season four, episode 11, called "Normal." Torres's detective assists the BAU as they track down The Road Warrior, a serial killer with a penchant for attacking women drivers on freeways in Orange County, CA.

In addition to Paul, another "Breaking Bad" alum made a guest appearance on "Criminal Minds." During season 10 of the show, Gunn portrayed an International Unit FBI agent, Lily Lambert, in episode 19, "Beyond Borders." The spinoff of the police drama had reportedly locked in Gunn's character as one of the leads of the show, but the actor later dropped out following the pilot.

Curry played arguably one of the most vicious unsubs in the history of "Criminal Minds": Billy Flynn. The brutal serial killer and rapist, notoriously dubbed The Prince of Darkness, would wipe out whole families during blackouts in California, leaving behind the children, who'd then be faced with the abject horror and trauma of finding their family members dead. His twisted and sick motives are enough to send shivers down anyone's spine. The English actor first appeared in the season five finale, "Our Darkest Hour," with a cliffhanger ending leading to his season six opening appearance in "The Longest Night."

Plaza terrorized viewers with her role as Cat Adams, a hit woman and a psychopath on a killing spree in the crime drama. The "Parks & Recreation" star first popped up in episode 11, "Entropy," of season 11 and went on to reprise the role in the two-part season 12 finale episodes before delivering a final appearance in episode six of the 15th season, "Date Night."

Adding to her stacked résumé, "The Great" actor also made a guest appearance on "Criminal Minds." In episodes six ("The Boogeyman") and 23 ("No Way Out, Part II: The Evilution of Frank") of season two, a young Fanning played Tracy Belle, a girl who escapes the attacks of a serial slasher, Jeffrey Charles (played by Cameron Monaghan), and another serial killer, Frank Breitkopf (Keith Carradine), by the skin of her teeth.

The "Mare of Easttown" actor also played a guest role in season five, episode 16 ("Mosley Lane") of "Criminal Minds." Peters played the young adult version of Charlie Hiliridge, a young boy who gets abducted at age 8 and later unwittingly ends up being an accomplice to the Roycewoods, a child-kidnapping couple. The BAU catch wind of the case and once again save the day as they rescue two other victims of the perpetrators.

The "Dawson's Creek" actor played a tech-savvy, DID-diagnosed serial killer, Tobias Hankel, in episodes 14 ("The Big Game") and 15 ("Revelations") of season two.