Parcells' first two comebacks worked out well: he led the Patriots to a Super Bowl in 1996, just three years after taking over as head coach, and Jerry Jones lured Parcells out of a three-year retirement in 2003 to coach the Cowboys to three winning seasons in four years. Success in his third comeback attempt, turning around Miami, which went 1-15 in 2007, might take longer.
After completing the second of the Bulls' two three-peats in 1998, Jackson walked away unsure if he would find another ''basketball challenge'' to accept. But after a year off, he returned to coach the Lakers, leading Shaq and Kobe to a three-peat from 2000 to '02 before stepping down two years later. Of course, he came back to L.A. again the following year, and reached the NBA Finals two seasons later.
The Rocket flirted with retirement before each of his three seasons with the Houston Astros and waited until May 2007 to announce his final comeback with the Yankees. Clemens won his seventh Cy Young after his first retirement in 2004, but his 2008 season netted just a 4.18 ERA and 6-6 record.
Jordan's first comeback, after a stint in minor league baseball, resulted in three straight championships for the Bulls. His second comeback brought a new uniform and a somewhat diminished image as the Washington Wizards missed the playoffs during both of Jordan's seasons.
With rumors circulating of a third failed drug test, Williams retired and sat out the 2004 season before returning to the Dolphins in 2005. He finished the season averaging 4.4 yards per carry with six touchdowns, but was later found to have tested positive for drugs again. While serving his one-year suspension, Williams played in Canada. He returned to the NFL in 2007, but suffered a season-ending injury just six carries into his first game back.
The New York State Boxing Commission forced Ali into early retirement at 25 when it revoked his boxing license for refusing to serve in the Army. Ali returned three years later to stage his epic trilogy with Joe Frazier, and returned from a second retirement at 37, only to get embarrassed by Larry Holmes.
After 10 years away from the ring, Foreman came back from his second retirement in 1988. In 1994, at 45, he reclaimed the heavyweight title he had lost to Muhammad Ali 20 years earlier.
A chronic wrist problem forced Howe to retire in 1971 after a 25-year NHL career, but he got back on the ice two years later for the newly formed World Hockey Association's Houston Aeros. At 51 he signed with the NHL's newest team, the Hartford Whalers, and scored 15 goals in 80 games while helping the Whalers make the playoffs.
The former heavyweight champ retired in 1986 after a second loss to light-heavyweight champion Michael Spinks. Lured by a $3 million payday, Holmes made a comeback to fight Mike Tyson in '88 but lost in a fourth-round knockout and retired again. Coming back in '91, Holmes would eventually lose title bids against Evander Holyfield ('92) and Oliver McCall ('95) before beating Eric "Butterbean" Esch in 2002. He retired for good at 52, ending his 29-year career with a 69-6 record.
Forced to leave hockey for two months after being diagnosed with Hodgkin's lymphoma in 1993, Lemieux returned to win the league's overall scoring record. Retiring again in '97, Lemieux maintained a position in the Penguins front office before returning to the ice in 2000 to finish with the league's best points-per-game average. Despite becoming the primary owner of the Penguins, Lemieux continued to play until his final retirement in '06.
In 1998, White retired after playing in two Super Bowls with the Green Bay Packers and being named NFL Defensive Player of the Year. Two years later he was back on the field as a Carolina Panther, finishing the season with six sacks and 16 tackles before retiring again.
No athlete is known for having more comebacks than Sugar Ray Leonard. His first retirement was in 1982 after he suffered a detached retina in his left eye. He returned a year later but re-retired after a fight with Kevin Howard. Leonard's next return, in '86, only lasted one fight as he beat Marvin Hagler in a split decision. In typical Leonard fashion, that retirement was only temporary and he came back in '88 before announcing two more retirements following loses to Terry Norris in '91 and Hector `Macho' Camacho in '97.