Criminal Minds is in its 14th season, and the format of the show has allowed for some notable guest stars over the years. Some have played the villain or the UnSub (or Unknown Subject) that the BAU (Behavioral Analysis Unit) is after, while others have played victims or characters connected to one of the team.
In most cases, these actors left their mark on the series, whether due to the character they played or just because of who they are. However, in some cases, fans may not have realized who was playing the role because the focus was on that character's impact on a team member, or maybe fans just forgot someone appeared in an early episode because the series has had over 300 episodes.
10 Aaron Paul
Before he became well known for his role as Jesse Pinkman on Breaking Bad, Aaron Paul appeared in Criminal Minds the Season 1 episode, "The Popular Kids" as Mike Zizzo. Mike was in his 20s but still hung out with high school kids. The group of them got high and listened to heavy metal and called themselves the Lords of Destruction.
The real UnSub, Corey, pointed the BAU in Mike's direction, framing him and his friends for murder. Paul has also appeared in other series including Big Love, The Path and BoJack Horseman.
9 Robert Englund
Everyone knows Robert Englund from his role as Freddy Krueger in the Nightmare on Elm Street movies, so it was only fitting that when he appeared on Criminal Minds, in one of its spookier episodes. However, his role wasn't as creepy as his the one he's most known for.
Englund played Detective Gassner in the Season 7 episode, "Heathridge Manor." The BAU investigated a woman found dead in an abandoned asylum. It was a fun bit of casting that allowed fans to make the spooky connection without putting him in the obvious role as the UnSub.
8 James Van Der Beek
If you know anything about WB shows, it's likely you recognize James Van Der Beek for his role as Dawson Leery on Dawson's Creek. He had arguably one of the most memorable roles on Criminal Minds when he appeared in two Season 2 episodes called "The Big Game" and "Revelations."
However, it's possible you didn't realize he played Tobias Hankel because the focus wasn't necessarily on him, but rather on his effect on the series. It was Tobias' capturing and physical and psychological torment of Reid and how that affected Reid for episodes to come that made the most impact.
7 Cameron Monaghan
Now, Cameron Monaghan is known for his roles as Ian Gallagher on Shameless and Jerome and Jeremiah on Gotham. Before he was playing those creepy roles on the latter, he was one of Criminal Minds' younger UnSubs 12 years ago. He played Jeffrey Charles in "The Boogeyman."
The BAU originally profiled the UnSub as an adult. They soon discovered they were looking for a child just before Jeffrey could claim another victim, Tracy Belle, played by another familiar face: Elle Fanning.
6 Jason Alexander
It's likely you know Jason Alexander for his role as George Costanza on Seinfeld. He also appeared as an UnSub, Henry Grace, on Criminal Minds in Season 4. A narcissistic psychopath, he turned himself in to Reid and Rossi after they spoke to a college class. He challenged the team to find five victims before it was too late and they died.
Henry thought in doing so, he would prove he was better than they were. He was wrong, and the team saved all five victims and themselves after he tried to rig a trap for the agents.
5 Tim Curry
You probably know Tim Curry for his roles in Clue and The Rocky Horror Picture Show, among many, many others, but those two are his most notable.
Unfortunately, his appearances on Criminal Minds were the opposite. He was entertaining in the role, but it was a dark one. He played the ominous UnSub Billy Flynn, a serial killer in two episodes. His story began in the Season 5 finale, "Our Darkest Hour," and served as the cliffhanger, which was then concluded in the Season 6 premiere, "The Longest Night."
4 Mark Hamill
Mark Hamill is best known for playing Luke Skywalker in the Star Wars movies, but you may not have realized that he also appeared in two episodes of Criminal Minds. He played John Curtis in the Season 8 episodes, "Brothers Hotchner" and "The Replicator." Curtis was the answer of the season-long mystery of the UnSub and stalker of the BAU, the Replicator. He was also responsible for killing Erin Strauss, the BAU Section Chief.
Though the Replicator was around for the entire season, he only appeared in those final two episodes, so it's understandable if he's not the first UnSub or actor you think of when you think of the series.
3 Gina Torres
Gina Torres is probably best known for her roles on Firefly and Suits (and soon to be Pearson) and in The Matrix movies. The 11th episode of Season 4, "Normal," featured a couple of notable guest stars. You likely recognized The X-Files' Mitch Pileggi as the UnSub, Norman Hill, a killer who also took the lives of his own family.
But did you realize that the detective who helped the BAU out with the case, Thea Salinas, was played by Torres? With the focus on the UnSub, especially once they realized what he'd done, it's not surprising if you forgot she appeared.
2 Bellamy Young
You likely know Bellamy Young for her role as Mellie Grant on Scandal. Maybe you saw her in several episodes of CSI: Miami or Scrubs. However, she also appeared in seven episodes of Criminal Minds, in Seasons 7 and 8. She recurred as Beth Clemmons, a love interest of Thomas Gibson's Aaron Hotchner.
They first crossed paths when they were training for triathlons and began dating, and she got along well with his son. However, Beth and Hotch weren't meant to last, as their relationship ended off-screen, likely due to Young's work on Scandal.
1 Tricia Helfer
You probably know Tricia Helfer best for her role as Number Six on Battlestar Galactica or more recently as Charlotte on Lucifer. She also appeared in the two-part Season 7 finale, "Hit" and "Run," of Criminal Minds. She played Izzy Rogers, a psychopathic killer, bomber, and bank robber.
She led a group of bank robbers who hit a bank in the D.C. area and held JJ's husband, Will, hostage. She insisted he let her into his home, but JJ was able to subdue her and keep her family safe.