There aren't too many times when an actor is replaced on a TV show for the same role. On occasion, you get pilots that are shot where an actor is later replaced, such as Lauren Graham replacing Maura Tierney on "Parenthood."
But once a show is established, if for some reason the actor leaves or dies, the character also leaves the show and is replaced by a different character.
There are a few notable exceptions: Dick Sargent replaced Dick York as Darren on "Bewitched;" Sarah Chalke replaced Lecy Gorenson on "Roseanne" for a season; and Barbara Bel Geddes was replaced by Donna Reid on "Dallas" for a season. In the latter two cases, producers came to terms with the original actresses after fans decried the change.
It's a heckuva lot harder to replace an actor in the same role, because it invites inevitable comparisons. And since the original actor created how the character is portrayed, the replacement's job is twice as difficult.
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Normally, it's better to simply replace the character, such as bringing in Jimmy Smits to play Bobby Simone on "NYPD Blue" and dumping the lead character of John Kelly after David Caruso and the producers parted ways on less-than-amicable terms.
Sometimes, though, that's not an option. Which brings us to "Spartacus" (STARZ, 10 p.m.), which returns for a new season tonight with Liam McIntyre replacing Andy Whitfield in the title role on the network's biggest hit.
Whitfield originated the role in the first season, then was diagnosed with lymphoma. At first, the actor responded well enough to treatments that STARZ and the producers did the unusual move of shooting a prequel miniseries for "Spartacus" to keep the show going but giving Whitfield a chance to recover and return to the role.
Unfortunately and tragically, Whitfield's cancer returned and it became clear that he couldn't continue. It left everyone in a difficult spot, because in addition to the logistics of replacing a popular lead, there was also the cast and crew's respect for Whitfield.
But the actor gave his blessing for both the production to continue and to his replacement, Liam McIntyre, who debuts tonight under the most difficult circumstances imaginable, since Whitfield died only a few months later.
Now McIntyre has to step into the lead role, a tough task in of itself, and replace an actor beloved by fans. Some fans will dismiss him out of hand, which I think is a shame -- McIntyre had little to do with anything that transpired, and was nothing but respectful to Whitfield.
Meanwhile, "Spartacus" fans will at least be assured of the usual amounts of blood, violence and sex that the series has so far provided.
WEEKEND'S BEST BETS: Farewell, "Chuck" (NBC, 8 p.m.) The spy comedy wraps up with a two-hour finale. "Chuck" started out as a clever, fun show but sort of lost its way -- it became something of the same joke over and over. The original idea wasn't sustainable, but turning Chuck (Zachary Levi) into a superspy made the rest of his team somewhat superfluous. I don't know, I guess I'm glad the series is wrapping up on its own terms, but I haven't been glued to it for a while.
Tonight's "Shark Tank" (ABC, 8 p.m.) has a smart idea for a business rejected and a dumb idea for one accepted. I'll leave you to figure out which is which.
Fox has a new episode of "Fringe" at 9 p.m., while "Merlin" is new at 10 p.m. on SyFy.
On Saturday, "The Fades" (BBC America, 9 p.m.) is new.
On Sunday, Wendi Scott-Carr's case against Will Gardner comes to a head on "The Good Wife" (CBS, 9 p.m.), but it's Eli Gold's rant to guest star Amy Sedaris about why following the teachings of Sun Tzu is wrong that's the episode's highlight, at least for me. It's followed by "CSI: Miami" at 10 p.m.
ABC is all new with "Once Upon A Time," followed by the Hallmark movie, "A Smile as Big as the Moon," while Fox has a new night of animation. NBC airs the Pro Bowl.
PBS continues "Masterpiece" (PBS, 9 p.m.) with the latest "Downton Abbey."
On cable, HBO debuts "Luck" at 9 p.m., while Showtime has new episodes of "Shameless," "House of Lies" and "Californication."