She was born in Tigard, OR, a suburb of Portland, to Don Olson, onetime publisher of the Portland Tribune newspaper. A shy girl growing up, she discovered an outlet in her preteen years, participating in shows and pageants put on at summer camp. A near-tragedy at age 12 accelerated her inclination towards the stage, when a serious bicycle accident left Kaitlin with a fractured skull. It required she undergo extensive reconstructive surgery, resulting in her starting her first year of junior high with a shorn skull, heightening her social awkwardness. Never a popular girl, by her own later recollection, she nevertheless broke out of her shell by way of speech and drama classes and displaying her self-effacing humor, even as she remained a quiet, inward student. She attended the University of Oregon, where she became a perennial lead in school stage productions, and, upon graduating, moved to Los Angeles in search of acting jobs.The new L.A. resident soon won a coveted spot in the famed Groundlings sketch-comedy repertory, performing weekly with its Sunday Company for a year. In 2000, she scored work in two ultra-indie films, "Jacks" and "Eyes to Heaven," and a bit part in the widely panned pseudo-sexploitation flick, "Coyote Ugly." She landed her first TV job on the neurotic HBO comedy "Curb Your Enthusiasm" (2000-), playing the Christian sister-in-law whose piety often abrades the show's Jewish protagonist Larry David. She would go on to reprise the character periodically over the next decade. Olson also won a spot on the short-lived Fox proto-reality show "Marks" (2002), and managed to net some TV guest roles on a couple of post-"Candid Camera" prank shows, "Punk'd" (MTV, 2003-07) and "The Jamie Kennedy Experiment" (The WB, 2002-03). Olson found more regular work when she scored a recurring role on ABC's most popular sitcom at the time, "The Drew Carey Show," playing the snippy, scheming girlfriend of the boss at Drew's new dot.com retailer job. The Carey association would afford Olson work after the sitcom shuttered, as she joined him for his improv-oriented "Green Screen Show" (2004) for its short run on The WB, and also joined Carey and his affiliated improv rep doing USO trips for U.S. troops in Kosovo and Bosnia. She returned to sketch-comedy briefly in the short-lived Fox mid-season replacement series "Kelsey Grammer Presents: The Sketch Show" (2005). Soon, however, her life was about to change.In 2005, she auditioned for a prospective comedy show being put together by struggling actors Rob McElhenney, Charlie Day and Glenn Howerton, which would chronicle the foibles of down-and-out and not necessarily likable actors in L.A., which they called "It's Always Sunny on TV." McElhenney, Day and Howerton had shopped a camcorder-shot pilot to the networks and found a home for it on News Corp's FX cable channel, then in the process of rebranding itself as a basic-cable repository of edgy original programming. They reset the show in McElhenney's native Philadelphia, where they would shoot exteriors, and the creators cast themselves as three of the show's central quartet, operators of a bar in South Philly, with McElhenney playing Mac, the ever-randy, macho pseudo-reactionary one of the bunch; Howerton as Dennis, the vain, semi-sophisticated but ultimately vapid one; Day as "Charlie," their dimwitted, borderline illiterate janitor and punching bag. Olson won the part of Dennis' sister Dee (aka "Sweet Dee"), a flustered, gawky would-be actress, somewhat more grounded than the others, but equally insecure and shamelessly manipulative - the four to be referred to collectively as "The Gang."Premiering in August 2005, "It's Always Sunny in Philadelphia" followed the foursome into shenanigans as unseemly, depraved and cynical as had been seen on television - one episode saw Dee and Dennis deliberately addicting themselves to crack so they could collect welfare payments - all set to chipper string music that hearkened back to lily-white family sitcoms of TV's Golden Age. Though it debuted to mixed reviews and meager ratings, the show developed a frenzied buzz, especially among young adult viewers, and though FX execs initially balked, they renewed "Sunny" for another season when fan of the show Danny DeVito agreed to join the cast as Dennis and Dee's prodigal (and equally amoral) father, Frank. The show became one of the top draws on FX on the strength of the Gang's inane, degenerate schemes, as evidenced in such jaunty episode titles as "Mac Bangs Dennis' Mom," "The Gang Exploits the Mortgage Crisis" and "Sweet Dee's Dating a Retarded Person."Along the way, McElhenney and Olson began dating and, in 2008, they married. Between seasons, Olson scored some supporting film roles, as in the snappy 2009 indie comedy "Weather Girl" and in the 2010 studio romantic comedy, "Leap Year." In 2009, the "Sunny" crew took on tour an expanded version of their offbeat musical episode, "The Nightman Cometh," playing theatrical venues in New York, Boston, San Francisco, Los Angeles and Philadelphia. Also that year, Olson's pregnancy by McElhenney was written in to the show as a mystery in which other members of "The Gang" fear they may be the father. The real-life couple had a son in September 2010, with Olson going into labor while they attended a Philadelphia Phillies-L.A. Dodgers game. Not surprisingly, the cast became major celebrities in Philadelphia, and McElhenney and Olson - in a case of life imitating art - opened their own bar, Mac's Tavern, in the city's Old Towne neighborhood in 2010. Olson moved into voice work with supporting roles in two adult-oriented animated series, National Parks-set workplace comedy "Brickleberry" (Comedy Central 2012) and suburban teen satire "Unsupervised" (FX 2012), co-created by and co-starring her "Sunny" cohort David Hornsby. Olson next appeared on the big screen in a small but memorable role as Tatiana, an Eastern European prostitute, in the action comedy hit "The Heat" (2013).