11 Guest Stars You Might Have Forgotten Were on Criminal Minds

Lynch has only appeared in a few episodes of the show, but her presence has been much bigger: she plays Diana Reid, Spencer's schizophrenic mother.

Before Monaghan starred on Shameless and Gotham, he was a child actor with a deeply creepy role on Criminal Minds as a serial killer who happens to be a young boy.

Van Der Beek had a two-episode arc as a serial killer with a split personality, which also briefly reunited him with former Dawson's Creek costar Meredith Monroe.

Muniz was fresh off his comedic role on the sitcom Malcolm in the Middle when he guest starred on Criminal Minds. His character was a massively traumatized crime victim who ends up becoming a serial killer himself.

Alexander's role here is a far cry from Seinfeld. At first, he plays a brilliant professor who seems to be on the same side as the BAU, but turns out to be much more sinister.

Before she was Scandal's first lady, Young had an eight-episode arc as Beth Clemmons, whose connection with Hotchner came after a devastating tragedy.

Trachtenberg guest starred in a deeply unsettling role as a terrifying stalker who ended up killing Dr. Reid's girlfriend Maeve.

Savage's guest role was something of an unusual one. Instead of playing a one-off character, he played the younger version of an existing main character: Jason Gideon, played regularly by Mandy Patinkin.

If you're expecting Plaza's role to be something even remotely close to Parks and Recreation's April Ludgate, you're in for quite a shock. Her Criminal Minds role saw her play a cold-blooded assassin who's behind multiple plots against Reid.