INDIANAPOLIS - Al Unser Jr. gave his heart to racing. When he felt his passion was gone, he had only one choice - to get out of the car.

On Wednesday, Unser, a two-time Indianapolis 500 winner, announced his retirement from the sport that defined his life and his family's legacy.

"I've had a great career," he said. "It's been a challenge, been hard to follow in the footsteps that I've followed. I feel I upheld the Unser name quite well."

Unser, 42, was one of open-wheel racing's brightest stars and biggest names during a turbulent time. He stayed with Roger Penske's team when the Indy Racing League and CART parted ways in 1996, then switched to the IRL in 2000.

Through it all, Unser was one of the few players who seemed to stay above the spat. He won two Indy titles, two CART points championships, a combined 34 races in 21 seasons and remained a favorite of fans and drivers.

"You knew if you were racing against Junior he'd try to pass you cleanly," former driver Scott Goodyear said.

The Unsers always considered racing a family business.

Junior started in go-karts at age 9 and learned his trade from some of the best. His father, Al, is one of three drivers with four Indianapolis 500 wins.

Junior's uncle, Bobby, won three times at Indianapolis, and Junior's two victories gave the family nine in the biggest race in open-wheel racing.

Two of Unser's cousins, Robby and Johnny, also raced at Indianapolis.

But after 33 summers of racing, Junior still couldn't leave the track completely.

His newest career - serving as an adviser for Patrick Racing, his team, and a driving mentor for his 21-year-old son, Al - begins this weekend at the Argent Mortgage Indy 300 in Kansas City, Kan.

Team owner U.E. "Pat" Patrick has not chosen a replacement for Junior.

"What scares me is going to Kansas this weekend and watching Little Al get out there," Junior said. "Hopefully, he can follow in his father's footsteps and his grandfather's footsteps."

The IRL has lost two of its most prominent drivers in 13 months. Michael Andretti retired in May 2003 at age 40.

Andretti also grew up in a racing family, endured the pressure of living up to his famous father's achievements and left the sport earlier than some expected to focus on his ownership in Andretti-Green Racing.

Michael's father, Mario, won the 1969 Indy 500 and 1978 Formula One title.

The two sons were continually linked, though, sometimes referred to as the IRL's second generation of stars.

"Al is one of the best guys that's ever driven a race car," Michael Andretti said in a written statement.

This season, Unser has dealt with a litany of frustrations.

He worked for several months to find a ride after breaking his pelvis last October when he was thrown from an all-terrain vehicle in New Mexico. After months of rehabilitation, Unser finally signed with Patrick Racing in March but missed the first three races of the IRL season.

In three starts, Unser's best finish was 11th, and last weekend at Richmond he was the slowest qualifier in the field. Unser finished 22nd in what proved to be his final race.

"I'd still like to see him racing, but if he's not happy, he should get out," his father said. "He's proven he's a champion."

Junior became the youngest driver, at age 24, to win the International Race of Champions series. He recaptured the title two years later. In 1992 and 1994, he won the Indy 500.

His most memorable season, though, was 1985, when he lost the CART title by one point to his father.

"That was a magical season," Junior said.

The tradition is now being handed down to a third generation.

Junior's son, Al, will make his Infiniti debut with Keith Duesenberg's team this weekend in Kansas City with his father watching.

"I'm happy for Al," Shelley Unser, Junior's ex-wife said. "I think this is a great opportunity for him to be more of a part of his children's lives. He has certainly missed out on a lot of what they've got going on."

Unser's life away from the track has been filled with travails.

He divorced his wife after 17 years and his daughter, Cody, contracted a rare disease that left her paralyzed from the chest down.

In 2002, Junior missed two races while staying at a treatment center for alcohol abuse following his arrest in Indianapolis after his girlfriend said he hit her in the face while drunk. Prosecutors didn't file charges.

Through it all, Unser focused on his driving.

But when Unser lost his passion, he fulfilled the promise he made to himself and retired.

"You just know when it's time," he said. "I never had set a date, but you have to have a passion for it. I'm no longer willing to maintain that level of sacrifice or desire."

AP-ES-07-01-04 0132EDT