'NYPD Blue'

Character: Detective John Kelly (David Caruso)

The story: A huge hit with the early audience of "NYPD Blue," Caruso's chivalrous but tough John Kelly was like every great hero out of detective fiction: the moral touchstone of an unpredictable and ceaselessly violent world. That's not to say Kelly wasn't compromised. A control freak that drove away his wife and enabled his alcoholic partner, Andy Sipowicz (Dennis Franz), Kelly even got romantically involved with a cop, Janice Licalsi (Amy Brenneman), who had been blackmailed to kill him. When the police department's "Rat Squad" (i.e., Internal Affairs Division) suspected Kelly of thwarting an investigation into possible crimes by Licalsi, he was forced out of his job.

Behind the scenes: Caruso had been busy in feature films ("King of New York") and television ("Hill Street Blues") for 13 years before the role of Kelly came along. The lure of bigger movies offered in the wake of the success of "NYPD Blue" proved too much, and he left.

The fallout: Fans who felt betrayed by Caruso's shockingly early exit after one season and four episodes of "NYPD Blue" stayed away from his next two features ("Kiss of Death" and "Jade"). "NYPD Blue," however, remained popular following the casting of Jimmy Smits as Sipowicz's new partner, Bobby Simone. During the series, all original major characters, except Sipowicz, left the show -- though Simone was written off most spectacularly, dying from heart disease over several wrenching episodes.

'24'

Character: Teri Bauer (Leslie Hope)

The story: In the final episode of the debut season, after a very bad day full of kidnappings and betrayals and setups and firefights, Jack Bauer (Keifer Sutherland) finds his wife, Teri, locked up and tied to a chair, with a bullet in her stomach.

Behind the scenes: Teri's death was part of the planned conclusion of the first season's story arc.

The fallout: The character's death was a factor in radically changing Jack's life, setting the stage for new developments in Season 2.

'Star Trek: The Next Generation'

Character: Tasha Yar (Denise Crosby)

The story: On the April 25, 1988, episode called "Skin of Evil," Security Chief Yar was killed by an inky, amorphous creature called Armus. Only 23 episodes into the new, Gene Roddenberry-created series, "Skin" concluded with a farewell to Tasha by the show's other regular characters.

Behind the scenes: Crosby, granddaughter of Bing Crosby, asked producers to write her off the show so she could accept movie roles.

The fallout: Crosby didn't get very far in any medium immediately following her departure from "Next Generation," though she started getting traction in episodic television again by the mid-1990s. "Star Trek" carried on without her, but it's also true she leaned on the series for occasional guest spots, prompting at least two of the series' writers to complain at "Trek" conventions about being Crosby's employment agency.  

'M*A*S*H'

Character: Col. Henry Blake (McLean Stevenson)

The story: On March 18, 1975, one of the most beloved characters on "M*A*S*H," Col. Blake, got his discharge from the U.S. Army and left Korea to go home. Henry's final scene was certainly traumatic (though funny). Just watching him go up in a chopper -- never to return to the mobile surgical hospital of which he had been in charge -- while Radar (Gary Burghoff) fought back tears was painful enough. What shocked millions of viewers came after the commercial break: Radar informed the other characters that Henry was killed when his plane was shot down over the Sea of Japan.

Behind the scenes: Stevenson was jumping networks to NBC, where he starred in "The McLean Stevenson Show" for a mere four months.

The fallout: Henry Blake's death took place during the Season 3 finale. When Season 4 premiered in the fall, the character of Trapper John (Wayne Rogers) was gone, too. That loss didn't quite hit between the eyes with the power of Henry's death, but taken together the departure of Trapper and Col. Blake ushered in a new era for the show.

'Lost'

Character: Boone Carlyle (Ian Somerhalder)

The story: Unexpected deaths are not uncommon on "Lost," but the first really caught fans by surprise. After a mishap with a plane found by Boone and Locke (Terry O'Quinn) in the forest, Boone is severely injured and takes an entire episode ("Do No Harm," first aired April 6, 2005) to die.

Behind the scenes: Boone's death was in the cards, though actor Somerhalder, as with other cast members written off the show, went to some lengths cooperating with producers in keeping the character's exit a secret.

The fallout: Tempers and suspicions rise among survivors following the killing of Boone, just when a planned escape for some grows imminent.

'Bonanza'

Character: Adam Cartwright (Pernell Roberts)

The story: The eldest son of Ponderosa top man Ben Cartwright (Lorne Greene) left the hugely popular "Bonanza" after the sixth season (1964-65), and without any farewell. The explanation for his absence was that Adam had gone off to college.

Behind the scenes: Pernell Roberts had tired of the role and was in disagreement with "Bonanza"'s writers about the character.

The fallout: "Bonanza" kept its large audience a few more years, but the loss of Adam -- scholarly and level headed -- threw off a careful, satisfying balance among Ben's three sons. (The other two were played by Michael Landon and Dan Blocker, whose death the summer before Season 14 also contributed to the demise of the show.)