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Simon Cowell on American Idol
It's no secret the Idol impresario wanted to bring his Leona Lewis-producing British hit The X-Factor to the States since he launched it. But we just never realized that he couldn't do both Fox shows at the same time. Come 2011, the only original judge left at the Idol table will be Randy Jackson. And that's a dawg-one shame.
2 of 10
Rosie O'Donnell on The View
The Queen of Nice turned nasty during her one-year stint on the buzzy morning gabfest — at least when she was dealing with co-host Elisabeth Hasselbeck. The clashes between the pair — most common during political discussions — were the stuff of legend, all leading up to their final, cable-news-style, split-screen smackdown on May 25, 2007. O'Donnell never returned to the show after that day, later saying in a video on her website: ''When I saw the split screen, that's when I knew it was over.''
3 of 10
Paula Abdul on American Idol
It was the tweet heard around the world: ''With sadness in my heart, I've decided not to return to IDOL,'' Abdul posted the evening of Aug. 4, 2009, letting fans know that her negotiations (sources say she refused a 30 percent pay raise) with television's biggest show were over.
4 of 10
Nicollette Sheridan on Desperate Housewives
Sheridan's Edie Britt always got the short shrift on Wisteria Lane — playing fifth fiddle to power-Housewives Susan, Bree, Gaby, and Lynette. But she managed to stick around nearly five seasons and survive a tornado and a hanging. But alas, it was a shocking car wreck and electrocution in April 2009 that eventually ended her time in Fairview.
5 of 10
T.R. Knight on Grey's Anatomy
Knowing that Knight — who'd been through the wringer with that whole Isaiah Washington scandal a few years before — was leaving Grey's wasn't the shocking part. It was how the medical soap's producers did it: mangling him so badly in a car wreck that it took his doctor friends at Seattle Grace hours to figure out it was him. His heaven-like elevator scene with Izzy (played by Knight's real-life bestie, Katherine Heigl) was a surprising — and truly memorable — send-off.
6 of 10
Jack Paar on the Tonight Show
On Feb. 11, 1960, the host abruptly walked off his own show, to protest NBC's censoring of a pre-taped segment. ''There must be a better way of making a living than this,'' he said as he left his desk — leaving his stunned announcer, Hugh Downs, to finish the broadcast. He returned to the show less than a month later. Why? ''When I walked off, I said there must be a better way of making a living,'' he explained to the audience. ''Well, I've looked...and there isn't.''
7 of 10
Kal Penn on House
Landing a starring role on the drama House was a big break for Penn, until then known largely for the stoner comedy Harold and Kumar Go to White Castle. But he walked away after less than two seasons, when he landed a job at the White House as associate director in the office of public liaison. Even more shocking than his decision to bolt the show? The way he left: The seemingly well-adjusted Kutner committed suicide with a shotgun, leaving fans (and House himself) stunned.
8 of 10
David Caruso on NYPD Blue
Caruso earned raves in 1994 for his turn as Det. John Kelly in the gritty, groundbreaking series NYPD Blue. But, thanks to his big-screen ambitions, he bailed on the hit show just four episodes into the second season. Alas, his movie career never took off, thanks to flops like Kiss of Death and Jade. (NYPD Blue, on the other hand, did just fine sans Caruso: He was replaced by Jimmy Smits, and the show ran until 2005.) These days, the actor is back in primetime, starring as Lt. Horatio Caine in CSI: Miami.
9 of 10
George Clooney on ER
ER made Clooney a star — but the actor walked away in 1999 to focus on his movie career. (Guess that worked out okay for him, huh?). Thank goodness the beloved Dr. Doug Ross reappeared for cameos in the 6th season — when he reunited with longtime love nurse Carol Hathaway (Julianna Margulies) and again in the 15th (and final) season.
10 of 10
Wayne Rodgers on M*A*S*H
After three seasons on the now-iconic military series, Rogers — the likable ladies man ''Trapper'' John McIntyre — grew weary of fighting for screen time with Alan Alda's Hawkeye. The show lasted 11 seasons (1972-1983) and won 14 Emmy Awards. ''If I had known it would run that long,'' Rogers reportedly admitted, ''I probably would have kept my mouth shut and stayed put.''