Matthew Gray Gubler, AJ Cook & Rest of 'Criminal Minds' Cast through the Years

Explosive series "Criminal Minds" is about to come to an end. Find out how the cast members and the characters they play have changed from its pilot episode till now.

"Criminal Minds" has been on for 15 seasons, and there has been a lot of changes in the cast. Those who play the characters fans love have evolved just as their roles have.

Throughout the airing of "Criminal Minds," cast members have come and gone. Some left to take on other projects while some characters were killed off. Despite these dynamics, some have remained from season one till the finals.

THE CONSTANTS

One of such is Matthew Gray Gruber, who plays the character of Dr. Spencer Reid. Coming on the show a little green eared, Matthew has proven himself to be a pro at playing his role.

Viewers have watched him change from being the socially awkward boy genius to being the not so awkward man genius. Another constant on the show is Kristen Vangsness.

Krestin plays the character of tech genius Penelope Garcia and has been on the show since its premiere in 2005. Her character is an interesting one because she doubles as a core member of the team and the comic relief.

A particular cast member in the person of AJ Cook has spent a significant portion of her life and career playing the delectable Jennifer Jareau, also known as JJ.

AJ joined the show since it began, at the age of 27, and at 41 years, the viewers have seen her transform into a convincing team member.

RETAINED ADD-ONS

Paget Brewster joined the series in season two and stayed till season seven. She plays the role of the current Chief of the unit, Emily Prentiss. After season seven, Paget took a break off CBS shows but returned in season twelve and has stayed on till the end.

Aisha Tyler mentioned it was a bittersweet experience.

Father figure David Rossi played by Joe Mantegna, joined the show in season three. Speaking of his experience on the show, Joe stated that it was an enjoyable experience, and he would miss playing the role of Rossi.

THOSE WHO LEFT

Flirtatious and suave character Derek Morgan played by Shemar Moore, had a long time on the show starting from season one through to season eleven, and fans were sad when his character had to leave as a regular. Shemar said his reason for leaving the show was:

"I love what I do for a living, I love it from 'action' to 'cut,' but I also want to walk my dogs, travel, get married, have kids."

From season one to season twelve, Thomas Gibbson played the role of Aaron Hotchner, a troubled workaholic agent. Thomas was subsequently fired from the show after an altercation on set, a decision he notably regrets.

OTHER NOTABLE CASTS

67-year-old Mandy Patinkin played the show's original lead in season one and two but left after the death of his on-screen girlfriend. Subsequently, the role of Jason Gideon, played by Mandy retired from the unit following the death.

Another notable cast is Aisha Tyler, who played the role of Dr. Tara Lewis. She joined the show in season eleven and has stayed on till the end. Interestingly, she even directed some episodes of the series. Speaking about the ending, she said it was a bittersweet experience.

The handsome Adam Rodriguez plays Luke Alvez's character. Adam joined the show in season 12 and is on till the very end. Taking over Derek Morgan's place at the unit, Luke has become a character fans cherish.

Daniel Henney portrays, Matthew Simmons. Matthew's character was first introduced in season thirteen and has remained till the end, with Matthew now being a significant character.