'Criminal Minds': See the Entire Cast Transform Over the Years

Season 1

The series began with Jason Gideon (Mandy Patinkin), Aaron Hotchner (Thomas Gison), Derek Morgan (Shemar Moore), Elle Greenaway (Lola Glaudini), Spencer Reid, (Matthew Gray Gubler) and Jennifer "JJ" Jareau (A. J. Cook) working together to help the BAU solve criminal cases, introducing fans to their world of FBI profiling.

Season 2

Season 2 brought the permanent arrival of Penelope Garcia (Kirsten Vangsness), the BAU's technical analyst who has since become a fan-favorite character. She was joined by agent Emily Prentiss (Paget Brewster), who joined the BAU after Greenaway's departure.

Season 3

The next season saw David Rossi (Joe Mantegna) join the team, becoming an integral member, with the show having delved into Rossi's personal and professional life throughout the seasons. Gideon left the show after Season 3 and was eventually killed off screen in Season 10 by a suspect from one of his early cases.

Season 6

The next major change for the BAU came with the arrival of Ashley Seaver (Rachel Nichols), who joined the agents after J.J. accepted a promotion at the Pentagon. Seaver stayed only for one season, with J.J. returning to the BAU in Season 7.

Season 8

FBI linguistics expert Alex Blake (Jeanne Tripplehorn) made an appearance at the BAU during seasons eight and nine, rejoining the team after Prentiss transferred to Interpol in London.

Season 10

In Season 10, former undercover agent Kate Callahan (Jennifer Love Hewitt) joined the group for one season. Hewitt's appearance coincided with the actress' real-life pregnancy, with the character of Kate discovering she was pregnant in the middle of the season and ultimately deciding to take a year off to raise her child.

Season 12

Season 12 saw several new cast members arrive including forensic psychologist Tara Lewis (Aisha Tyler), fugitive task force agent Luke Alvez (Adam Rodriguez) and agent Stephen Walker (Damon Gupton). Both Tara and Luke are still members of the team, while Stephen was only on the show for Season 12.

The season also saw the exit of Aaron Hotchner after the real-life firing of Thomas Gibson. Derek Morgan had also left the BAU after Season 11, though he has appeared as a guest in seasons 12 and 13. To offset his departure, Prentiss returned to the team after appearing as a guest in seasons 9 and 11.

Season 13

Matt Simmons (Daniel Henney) is the latest new member of the BAU, having appeared as a guest in seasons 10 and 12 and scoring a permanent spot during Season 13.

Photo Credit: Getty / CBS Photo Archive