Among Mummers, Bill Isaacs is known as "The Legend."

Fifty years ago, Isaacs helped found the Downtowners Fancy Brigade, leading the group to seven first prizes during his 21 years as captain. When, in the 1960s, he built a showboat around an old Packard and sent it rolling down Broad Street, he ignited the competition that brings bigger, wider, taller and more elaborate floats today.

Admirers say Isaacs is a visionary who changed the course of Mummers history.

"Just like in the NFL, when every few years there's a coach that comes along and changes the system, Bill changed the parade and the way of doing things," said Downtowners president Frankie DeVito, 42, of Washington Township. "Without him, we wouldn't be here, celebrating our 50th year."

On New Year's Day 2009, if all goes as planned, Isaacs will ride as Sitting Bull as the Downtowners present "Spirit of the Eagle." At 86, he will be the Downtowners' oldest participant - the youngest is 5 - and the appearance would mean he will have taken part in a Mummers Parade in every decade since the 1920s.

The only catch is Isaacs' health. He's been frail since a stroke a few years ago, and he missed a recent Downtowners practice.

Still, Downtowners captain Jim Julia said he wouldn't be surprised to see Isaacs rally for his club. A few years ago, Julia recalled, Isaacs was seriously ill and no one expected him to make it to events, but he did.

"He could hardly walk, but when he could, he'd walk into the club," Julia said.

In 1963, Isaacs, a carpenter, bought the Packard for $52 and transformed it into the first large float ever used, to go with the Downtowners' "Dixie Fantasy" theme.

"It completely changed the Fancy Brigades," said Julia, who is also president of the Fancy Brigade Association. "At that point, they were thought of as string bands without instruments. He changed that and they became known for the props and the storytelling."

It also ignited fierce competitions among the brigades.

"Each club that wanted to beat him had to learn to use props," Julia said. "It started with one prop, then two props, and now you have what you see in the Pennsylvania Convention Center."

Bill Harvey, who will perform with the Downtowners for the first time in 2009, went float-to-float against Isaacs for years when he was with the Strutters New Year's Brigade.

"He kept beating me. But one time, one time, I beat him," said Harvey, 68, of Wildwood. "When they made a rule, Billy found a way to get around it. If they said a float could only be so long, they didn't say how high it could be, or they didn't say how many 14-footers they could put together."

Isaacs' over-the-top creations are the stuff of Downtowners lore: The elephants he designed for "Genghis Khan," the mountain he built for "Close Enounters," the lighted stage he ordered for "Copacabana," the pirate ship that was so tall it couldn't fit under the wires suspended across the road, requiring the entire brigade to join together to tilt it underneath them.

As a captain, Isaacs was a strict disciplinarian who demanded a military-style drill. He once fined a member who missed two practices because of his honeymoon. "He shouldn't have gotten married in November," Isaacs reportedly said.

Even after he retired as captain, Isaacs watched practices and gave advice. In 2002, the last time the Downtowners won first place, Isaacs came to practice and suggested that Julia make a few changes to the performance. Julia said he initially balked, but took the advice.

"Is that why we won first? I don't know. But anything he ever says to me, I'll listen to," Julia said. "Last year, at 85, he was watching and he'd come up behind me and say, 'Third one down is off-time.' "

Nicky D'Alonzo, 37, recalled the first time he saw a ship - in the middle of Oregon Avenue. It was one of Isaacs' creations, but the young D'Alonzo thought it was the real thing.

"It looked like it had just come off the water," D'Alonzo said, recalling how his father lifted him aboard. "It wasn't a float to me. It was a ship."

D'Alonzo, now a Downtowners vice president, said Isaacs had an eerily accurate way of predicting months in advance how the club would perform on New Year's Day.

"From the time we picked the suit in February, he'll say, 'Third place,' and, sure enough, third place," D'Alonzo said. "Last time we got first, he came out with a broom and gave us a clean sweep."

Isaacs hasn't seen the 2009 costumes or routine. The Downtowners hope he can give them his stamp of approval on New Year's Day.

"No matter what, he'll be with us on our 50th anniversary," said Bob Galvin, 71, of South Philadelphia, who was cocaptain with Isaacs for 16 years. "He's our leader, our captain emeritus."