LOS ANGELES - As Disney Channel prepared to launch the cartoon series "Phineas and Ferb," one top company executive thought the hard, geometric shapes of the characters' heads represented too radical a departure from Disney's round-faced animation tradition.

But talk of forcing the creators to soften the edges of Phineas' isosceles dome to make him and the other angular characters less jarring was quelled.

"I said 'no,'" said Disney Channel Entertainment President Gary Marsh. "This is what I love about this show. It is different, and driven by someone's unique vision - as opposed to compacted by a committee."

Two seasons later, "Phineas and Ferb" has emerged as Disney Channel's first breakthrough original animated series, attracting more children and young teens than rival Nickelodeon's 11-year juggernaut "SpongeBob SquarePants," Nielsen Media Research reports.

In a sign of its growing significance, "Phineas and Ferb" is getting the full Disney treatment as the company revs up its well-oiled franchise machine. Soon it will uncork a full merchandise line, with 200 Phineas and Ferb-related items - including boxer shorts, skateboards and boxes of macaroni and cheese - headed to stores. A Disney Channel movie, "Phineas and Ferb: Across the Second Dimension," is scheduled for release next summer.

"I do believe that within the next 18 months, this will be one of the biggest properties that we've ever had," Marsh said.

That's hardly a modest goal from Disney Channel, which was the seedbed for billion-dollar entertainment properties such as "Hannah Montana" and "High School Musical." And the series - which follows the absurd lengths to which stepbrothers Phineas and Ferb will go to conquer boredom during their summer vacation - is earning the ultimate Hollywood validation: voice cameos by guest stars.

"Everybody and their mother wants to do this show," said Bonnie Liedtke, an agent with William Morris Endeavor. "We have requests from our clients to do the show because they watch it with their kids."

Among the stars who have recently lent their voices are Tina Fey, Ben Stiller, Seth MacFarlane, director Kevin Smith, and musicians Clay Aiken and Chaka Khan.

"It is a smart television series that does not play down to kids," said Toper Taylor, chief executive of Cookie Jar Entertainment, the creator of such PBS children's shows as "Arthur" and "Caillou." "Parents enjoy watching because there're a lot of jokes in the show for them."

"Phineas and Ferb" employs the same joke-a-minute sitcom pacing that make prime time cartoons such as Fox's "Family Guy" popular among adults, Taylor said. That reflects the pedigree of the creators, Dan Povenmire and Jeff "Swampy" Marsh, who have worked on "The Simpsons," "King of the Hill" and "Family Guy."

Indeed, Povenmire and Marsh incorporate sophisticated one-liners that would once provoke winces from network executives, such as the one about Existentialist Wacky Pack trading cards, in which one character remarks to the other, "I'll trade you two Nietzsche for a Sartre."

"They'd say, 'Is that joke too old for our audience?'" Povenmire said. "And we'd say, 'We don't care as long as that joke doesn't make the kids change the channel. There's a joke coming for them in five seconds. We're playing to the adults in the room.'"

To find another elusive hit for Disney Channel, Gary Marsh employed the same strategy he used when he took over the once-sleepy TV animation studio five years ago: He raided the competition and recruited an executive from Nickelodeon, Eric Coleman, who had championed such hits as "SpongeBob" and "Avatar."

The move was a tactful admission that Disney Channel didn't have people in-house to develop animation with a new sensibility.

Coleman now oversees "Phineas and Ferb" and is creating new series that borrow the elements he considers key to that series' success: a look that distinguishes it from other animation, a willingness to take risks and stories that revolve around characters he calls "confident misfits."

One new show debuting in the fall, "Fish Hooks," follows three aquatic characters who attend Freshwater High, a school in a giant fish tank in the center of a pet store. Coleman described it as a visually arresting collision of 2-D digital animation and photo collage.

"We are striving to be a generator of new content and new characters that can help fuel other parts of the business," Coleman said. "We have had tremendous success doing that on our live action side. We are excited about doing that in animation as well."

The sharp angles of "Phineas and Ferb," which Povenmire first sketched on a piece of butcher paper in a restaurant 16 years ago, kept it from finding a network home. The creators pitched other networks before Disney optioned it in 2005.

More than its look distinguished "Phineas and Ferb" from past Disney Channel animations, which, while under the control of the motion picture studio, relied heavily on TV adaptations of Disney animated films, including "Lilo & Stitch: The Series" and "The Emperor's New School."

Instead of starting with a script, the writers hand the storyboard artists an outline that plots the major story arc for the each episode.

The artists then flesh out the story, the gags and the illustrations through improvisation. Illustrators act out the episode, adopting each character's voice, as the accompanying animation displays on a whiteboard behind them in slideshow fashion. The creators say this process results in more action and unexpected humor.

The storyboard process initially produced anxiety among Disney executives accustomed to giving detailed notes on scripts, Marsh said, because it represented a loss of creative control. But success has a way of calming nerves.

"The great thing about Dan and Swampy is they are vigilant in protecting their vision," said Gary Marsh. "It makes for challenging notes sessions. But at the end of the day, we end up deferring to them because they've created something unique. The last thing that I want to do is dumb it down."