Muhammad Ali
Boxing always provides us with failed comeback stories, but unfortunately it is the greatest boxer of all time that takes the cake. When Ali retired in 1978 after regaining the WBA welterweight title from Leon Spinks he was on top of the world. Two years later at 38 he returned to the ring and was stopped by Larry Holmes in the 10th round – his first defeat in a fight that didn't go the distance. Another comeback a year later also failed when he lost to Trevor Berbick by a unanimous decision, just his fifth professional defeat. That would be his final bout.
Mark Spitz
The American was the greatest swimmer in Olympic history until Phelps eclipsed his record seven gold medals at a single Games in Beijing. Spits retired after his record haul at Munich in 1972, but launched an audacious bid to qualify for the 1992 Barcelona Games at age 41 after film maker Bud Greenspan offered him a million dollars if he succeeded in qualifying. He fell two seconds slower than the requisite qualifying time at the Olympic trials, although he did perform nearly as good as he did when he dominated the Munich Games.
Bjorn Borg
Considered one of the greatest tennis players of all time, the Swede stunned the tennis world when he retired in 1983 at age 26. By that stage of his career he had won five French Open titles and five Wimbledon crowns. Eight years later he boldly attempted a comeback. He used the same old wooden racquet, despite everyone else on tour using the modern graphite racquets. He failed to win a set in his first nine matches in 1991 and '92. He played three matches in 1993 – all losses – before finally calling it a day.
Michael Schumacher
Widely regarded as the greatest Formula One driver of all time, the seven-time champion retired in 2006 after a glittering career. The Ferrari legend agreed to return midway through 2009 as cover for the injured Felipe Massa, but he never raced due to a neck problem. He did return to the sport on a permanent basis from 2010 with the new Mercedes GP team. In three seasons, he finished on the podium just once before finally retiring aged 43.
Michael Jordan
The greatest basketball of all time had two comebacks, but we are looking at his failed career at the Washington Wizards, not his comeback after an unsuccessful stint in the MLB. After achieving everything there is to achieve in basketball, Jordan retired in 1999 just shy of his 36th birthday. Two years later he suited up for the Wizards. In his first season, he was solid despite a knee injury ruining his season. He averaged a career-low 20 points per game in his second and final NBA season and didn't feature in the post-season.
Brett Favre
The legendary quarterback is vying with John Farnham for the most comebacks. After 16 years with the Green Bay Packers, Favre formally announced his retirement for the first time in March 2008. After a messy departure from the Packers, Favre was eventually traded to the Jets. He had a relatively successful season, but in February 2009, he informed the franchise he would be retiring. But by August he had signed for another team, the Minnesota Vikings. He had a stunning season, leading the Vikings to the NFC Championship game but after struggling in the off-season he informed his team-mates he wouldn't be playing another season. Two weeks later he changed his tune AGAIN and played on. After the 2010 season and a host of individual records, the "Gunslinger" finally called it a day.
Tony Lockett
Plugger retired at the end of 1999 with 1357 goals to his name from 278 games with St Kilda and Sydney. It's a record that will never be broken. So why did a 36-year-old Lockett return for one final season in 2002? It's remarkable he even made it onto the park given how out of shape he was. Wearing the unfamiliar No.46, Lockett played three more games where had a grand total of five kicks, one mark and three goals.