Most everyone woke up to the sad news Sunday morning that “Glee” star Cory Monteith was found dead at the of age of 31. Monteith became an overnight sensation in 2009 on Fox’s musical-comedy series as Finn Hudson, a high school football star who becomes an integral member of the school’s glee club.

Over the decades, other regulars on TV series have also died suddenly. Here is a look at a few:

Larry Hagman

The actor was in his second season reprising his signature role of the ruthless J.R. Ewing on TNT’s reboot of “Dallas” when he died Nov. 23, 2012, of complications from cancer at the age of 81. The producers came up with a clever way for J.R.’s character to die in the series this past spring, which involved J.R. hatching a “beyond the grave” plan to implicate his nemesis Cliff Barnes.

Hagman’s death was not the only one that rocked the series. When it was enjoying enormous success on CBS more than 30 years ago, Jim Davis, who played J.R.’s dad, Jock, died of cancer on April 26, 1981, at the age of 71. Instead of killing off the character immediately, the producers had him away from the Southfork ranch, drilling for oil in South America. Finally in January 1982, Jock was declared dead in a helicopter crash.

PHOTOS: Cory Monteith dies; 'Glee' star was 31

Jon-Erik Hexum

The strapping, good-looking, 26-year-old actor was starring in the CBS detective series “Cover Up,” with Jennifer O’Neill. It had been on the air less than a month when, on Oct. 12, 1984, Hexum became bored during a long day of filming and, as a joke, put a .44 magnum prop gun to his temple and pulled the trigger. Tragically, the gun fired and the plastic wadding from the blank cartridge shattered his skull. Five hours of surgery ensued, but there was too much damage. He was taken off life support on Oct. 18.

Antony Hamilton was hired to replace Hexum and his first episode debuted a month later. The series, though, was history after one season.

Nicholas Colasanto

The character actor and TV director played the kind, sometimes forgetful bartender Ernie “Coach" Pantusso on the Emmy Award-winning NBC comedy series “Cheers.”

Colasanto died of a heart attack during the third season on Feb. 12, 1985, at the age of 61. The character’s death was addressed in the fourth season premiere, which also marked the debut of Woody Harrelson as his replacement, Woody Boyd, a naive young farm boy from Indiana who had been taking mail-order courses in bartending from Coach.

John Ritter

The popular actor, who shot to fame in ABC’s “Three’s Company,” was rehearsing an episode on Sept. 11, 2003, for the second season of his ABC sitcom “8 Simple Rules for Dating My Teenager Daughter” when he fell ill on the set. He died that evening of aortic dissection at the age of 54.

ABC aired the three episodes Ritter had already done. After a hiatus, James Garner and David Spade joined the cast and the show was retitled “8 Simple Rules.” It was canceled in 2005.

Phil Hartman

The former “Saturday Night Live” regular was starring as a pompous on-air anchor working at a news radio station on NBC’s sitcom “NewsRadio," when on May 28, 1998, his third wife, Brynn, shot and killed him while he was sleeping, then committed suicide. He was 49.

His character, Bill McNeal, was said to have died of a heart attack while watching TV. Another "SNL” regular, Jon Lovitz was brought in to play an on-air personality who had an insecurity problem. The series ended the following year.

PHOTOS: Celebrities who died young

Freddie Prinze