T.R. Knight (“Grey’s Anatomy”)

Fame: Knight’s character on “Anatomy,” Dr. George O’Malley, was being written out of the show by creator Shonda Rhimes in 2009, even though he was a fan favorite. Rhimes eventually confessed that she was subtly — or at least as subtly as “Grey’s Anatomy” can get — trying to prepare fans for a season finale involving O’Malley getting hit by a bus, but Knight had no idea, and was pissed that he only appeared on-screen for a total of 48 minutes in the first nine episodes of Season 5 (the two had “trust problems”). So, instead of asking Rhimes what was going on, Knight simply asked to leave. And he was hit by a bus.

Since Then: Well, I once got to interview him and Patrick Stewart when the two were doing press for A Life in the Theatre on Broadway. He seemed like a swell guy, and, um, that’s about it. As for “Grey’s Anatomy,” it sucked then and it sucks now, but women still watch it, so bad call, T.R.

Ellen Cleghorne (“Saturday Night Live”)

Fame: In 1991, Cleghorne became only the second African-American female repertory player, i.e. not featured, on “Saturday Night Live” (trivia: who was the first?), with a specialty of celebrity impressions that Kenan Thompson would probably be forced to do today, including Tina Turner, Whoopi Goldberg, and Toni Morrison. [Editor's Note: Thompson does indeed portray Whoopi] After “Saturday Night Live’s” painfully unfunny 1994-1995 season, Cleghorne quit the show, thinking she could be more successful with a sitcom of her own, the modestly-title “Cleghorne!” It lasted one season on the WB. (Fun fact: its penultimate episode was named “Money for Nothing and Your Chicken for Free.”)

Since Then: She’s basically disappeared. Playing “Uncredited” in Old School hasn’t done much for her career, and according to IMDb, she hasn’t appeared in anything since 2007’s Mattie Fresno and the Holoflux Universe, the unofficial sequel to Joseph and the Technicolor Dreamcoat. But Cleghorne will always have a special place in my heart: as Bus Driver Sally in “The Adventures of Pete and Pete.”

Joe Piscopo (“Saturday Night Live”)

Fame: “This story begins in the unforgettable spring of 1983. Ms. Pacman struck a blow for women’s rights, and a young Joe Piscopo taught us how to laugh.” Piscopo joined the cast of “Saturday Night Live” in 1980, and he and Eddie Murphy quickly became the show’s breakout stars (here’s a brilliant clip of them impersonating Frank Sinatra and Stevie Wonder). They also both left the show in 1984 in search of big-time movie careers.

Since Then: “It all happened during the magical summer of 1985. A maturing Joe Piscopo left ‘Saturday Night Live’ to conquer Hollywood; People Express introduced a generation of hicks to plane travel; and I was in a barbershop quartet.” Unlike Murphy, who would soon star in Beverly Hills Cop, Raw, and Coming to America, Piscopo’s career quickly bombed with movies like Johnny Dangerously and Sidekicks, where he played an evil dojo store owner. He has since been accused of having a steroid addiction, and his career has become a punch line for “Family Guy”, Tom Petty, “Psych”, and, yes, “The Simpsons.”

Honorable Mention!

Toby Huss (“The Adventures of Pete and Pete”)

Fame: It wasn’t exactly a big hit at the time, but for millions of nostalgic twentysomethings like myself, “The Adventures of Pete and Pete” was one of the greatest things to come out of the 1990s, along with Pavement and Topanga from “Boy Meets World.” He left the show near the end of Season 2 with the two-part episode “Farewell, My Little Viking,” where the Strongest Man…in the World! goes off to befriend another young boy in need of a superhero (in retrospect, that’s pretty disturbing, actually).

Since Then: Huss has gotten steady work since, including voicing Cotton on “King of the Hill” and as the Robber in an episode of “Bob’s Burgers” from earlier this year, but he’ll never top Artie, who taught me how to dance the Voodoo Crispy.