Chloe O'Brian is a fictional character played by actress Mary Lynn Rajskub on the US television series 24. An analyst at CTU Los Angeles, she is Jack Bauer's most trusted colleague, often doing unconventional and unauthorized favors for him, even at personal risk to herself. As O'Brian, Rajskub appeared in 125 episodes of 24, more than any other actor except series star Kiefer Sutherland, who appeared in all 204 episodes of the series. UGO.com named her one of the best TV nerds. AOL named her one of the 100 Most Memorable Female TV Characters.

Mary Lynn Rajskub is an American actress and comedian who is best known for portraying Chloe O'Brian in the action thriller series 24 and Gail the Snail in It's Always Sunny in Philadelphia. Rajskub was a regular cast member on HBO's Mr. Show with Bob and David, appeared in The Larry Sanders Show, Brooklyn Nine Nine, and Veronica's Closet, and such films as Dude, Where's My Car?, Firewall, Sweet Home Alabama, Punch-Drunk Love, Mysterious Skin, Little Miss Sunshine, Sunshine Cleaning, Safety Not Guaranteed, and The Kings of Summer, among others.