Robin Williams played a genie. Ellen DeGeneres landed a role as a fish. And now Joaquin Phoenix is starring as a bear.

They didn't don sweaty costumes or sit through hours of grueling makeup. The actors have all lent their voices to animated films.

Having established stars contribute their oral talents to an animated movie can help boost a picture's bottom line by bringing in more adult fans, and add luster to a celebrity's resume.

"It's about box office, of course," said Coury Turczyn, editor of PopCult, an online popular culture magazine. "It's just the fail-safe choice of every studio executive: When in doubt, go with a celebrity."

In "Brother Bear" — which opens in New York and Los Angeles Friday and in the rest of the country Nov. 1 — the star power behind the animated characters includes actors Joaquin Phoenix, Rick Moranis, Michael Clarke Duncan and Estelle Harris (search), known for her role as George Costanza's shrill mother on "Seinfeld."

At one time, trained voice actors were recruited to give life to animated characters, but the trend of using familiar voices — and faces — is definitely on the rise, according to John Canemaker, director of animation studies at NYU's Tisch School of the Arts (search).

That's put the careers of seasoned voice actors in jeopardy.

"There's a Mel Blanc (search) out there who's not going to get work because studios would rather go with a celebrity voice," said Turczyn, referring to the man who did voices for Bugs Bunny, Porky Pig, Daffy Duck and other characters.

The pull of celebrity recognition isn't limited to how the characters sound. Canemaker said animators often incorporate stars' features and gestures into their drawings so they resemble the actors who play them.

"You can build on that known personality and caricature the animation," he said. "It's successful. People seem to like it."

People meaning the adult chaperones, of course, since most children aren't exactly star-watchers.

"If it's a movie that might be of limited appeal to adults, (studios) think, 'We've got to somehow get them into the theaters and bring their kids,'" said Turczyn. "I don't know if an 8-year-old is going to care that Brad Pitt is the voice of Sinbad, but the parents might."

That's exactly what led Pennsylvania mother Laura Leptuck to take her 4-year-old daughter, Sarah, to see "Sinbad: Legend of the Seven Seas."

"If I hadn't heard that he was the lead, I probably wouldn't have even known the film was out," said Leptuck, 32.

Though she generally chooses animated films based on whether she thinks her daughter will like them, Leptuck said that star voices can make the movies more appealing to her.

"As I sit through it, I can picture the person doing the voice," she said. "It makes it more interesting for me."

But the practice can backfire — as it did with "Sinbad," which most Brad Pitt fans apparently avoided. The movie was a major flop at the box office.

"It can be absolutely dreadful when they cast purely for name value as opposed to voice acting ability," said Turczyn. "Everybody thinks Brad Pitt is adorable and lovable and hot, but when you just use his voice, which is not necessarily an emotive voice, it kind of falls flat."

Other times, however, studios manage to choose just the right celebrities to do the characters — as they did with Williams in "Aladdin," Whoopi Goldberg in "The Lion King" (she did the voice of a hyena) and DeGeneres as the blue fish in "Finding Nemo."

In fact, the major star power and talent of DeGeneres, Albert Brooks, Geoffrey Rush and Willem Dafoe helped make "Nemo" one of the most successful movies of 2003.

"When you cast stars who really have the ability to inject personality and emotion in their voices, it works out really well," said Turczyn. "You can look to any of the Pixar (search) movies for examples. They have the ability to find just the right star for the character."

Though voice work tends to bring in nominal pay, it can add polish to celebrities' careers in other ways — making them look simultaneously versatile and family-friendly. But Turczyn is skeptical of their intentions.

"They do it for their image," he said. "They want to make it look like they're doing something for the kids."