I mean, let’s start at the top - with Muhammad Ali. Although this is a tale with two endings.

Shortly after winning the world heavyweight boxing title in 1964 as Cassius Clay, he took up the Muslim faith and changed his name, subsequently refusing to be drafted into the military due to his religious beliefs and ethical opposition to the Vietnam War.

In 1967 he was convicted of draft evasion and stripped of his titles, and although he managed to stay out of prison his appeal to the Supreme Court was only accepted in 1971 - by which time he had missed what, for mortals, would have been the prime years of his career.

Ali came back from not so much retirement as exile to win some of the greatest fights ever, having revenge on Joe Frazier in 1974, in the self-styled Thrilla in Manila, and regaining the world title in the extraordinary defeat of George Foreman in Zaire - the Rumble in the Jungle.

In 1979, Muhammad Ali retired having become the first man to win the heavyweight championship three times. But he couldn’t stay retired. Soon afterwards, already showing what subsequently appeared to be signs of Parkinson’s disease, he was heavily defeated by Larry Holmes in 1980, and went on to suffer further punishment in a defeat by Trevor Berbick in 1981.

Foreman, who retired in 1977, managed his own successful comeback after a decade out of the ring, eventually regaining the world title with a knock-out win over Michael Moorer in 1994.

Michael Phelps was another hugely high-profile sportsman who managed a successful comeback. Having retired from swimming aged 27 after the London 2012 Olympics with 22 medals, 18 of them gold, making him the most-decorated Olympian ever, Phelps underwent struggles with depression.

He returned to the sport in 2014 and earned six more Olympic medals - five of them gold - at the Rio 2016 Games before retiring for good.

For Canadian ice hockey legend Mario Lemieux there was also golden Olympic success after a decision to come out of retirement.

Lemieux quit the game in 1997 after he had led the Pittsburgh Penguins to two Stanley Cups in the early 1990s and overcome Hodgkin's lymphoma and severe back injuries to become one of the National Hockey League's greatest scorers.  

But he returned to the fray in 2000, playing six more seasons and helping his country win Olympic gold at the Salt Lake City 2002 Winter Games.

Another notable "second career" within ice hockey was enjoyed by goalie Dominik Hašek, who hung up his skates in 2002, at the age of 37, having helped Detroit Red Wings win what had been an elusive Stanley Cup victory.

At that point Hašek had twice been voted as the National Hockey League’s most valuable player and had been a massive factor in the Czech Republic upsetting the odds to win Olympic gold at the 1998 Nagano Winter Games.

But the goaltender still had goals unfulfilled, returning to the Red Wings the following year and playing on until 2008 when, aged 43, he helped them earn another Stanley Cup victory.

Niki Lauda's Formula One career was marked by more than one retirement - although after a horrific crash at the 1976 German Grand Prix in which he barely survived and suffered extensive burns, he was away from the track for a barely credible six weeks, returning to complete the defence of his title and failing by a margin of just one point.

The following season he won his second title with Ferrari before moving to Brabham. But during practice for the 1979 Canadian Grand Prix he cut short a practice session and informed team principal Bernie Ecclestone that he wished to retire immediately, as he had no more desire to "continue the silliness of driving around in circles".

Lauda returned to Austria to run the charter airline he had founded Lauda Air.

But in 1982 he was back, this time with McLaren, and earned a third world title in his first season for his new team before retiring for good in 1985.

Belgium's Kim Clijsters was a notable high-achieving post-retiree in women’s tennis. She first called it a day in 2007, aged 23, having been world number one and won the US Open in 2005. But after getting married and starting a family she returned to the game in 2009 and won her second US Open title as an unseeded player in only her third tournament back.

She retained her title the following year, and added an Australian Open title in 2011, which put her back in the world No.1 position.

Dara Torres of the United States put together an extraordinary swimming career which earned her 12 Olympic medals over a quarter of a century.

After winning 4x100m freestyle gold at the Los Angeles 1984 Games and 4x100m medley silver at the Seoul 1988 Games she briefly retired before returning in the Barcelona 1992 Games, where she won another gold in the 4x100m relay.

She then took took seven years off before returning, aged 33, for the Sydney 2000 Olympics - where she won 4x100 gold in the medley and freestyle events, and took three individual bronze medals.

Eight years later she secured a place at the 2008 Beijing Olympics at the age of 41 and volunteered for a new enhanced drug-testing programme run by the United States Anti-Doping Agency, saying: "I want to be an open book, I want people to know that I’m 41 and I’m doing this right. I’m clean."

In Beijing she won two more silvers in the 4x100m freestyle and medley events, adding a third silver in the 50m freestyle. After missing out narrowly on qualifying to swim in a sixth Olympics at the London 2012 Games, Torres - finally - retired.

Britain's Sharron Davies was another notable Olympic women's swimmer to make a significant comeback. Her first retirement came aged 18 after a career that had seen her win two European bronzes, Commonwealth titles in the 200m and 400m medley and, at the Moscow 1980 Olympics, a silver in the 400m medley behind an East German swimmer, Petra Scheider, who later admitted that she had been part of her country’s institutional doping regime at the time.

Davies developed a successful TV and media career before going back into training in 1989 ahead of the 1990 Commonwealth Games in Auckland, at which she won her fifth and sixth medals in the event, taking silver in the 4x200m freestyle and bronze in the 4x100m freestyle.

Dara Torres wasn't the only outstanding female swimmer from the United States to seek a comeback at the London 2012 Games. Having retired after the 1996 Atlanta Games, Janet Evans, a four-time Olympic gold medallist, competed at the 2012 Olympic trials, but failed to qualify.

Sometimes the comeback is good without being quite as good.  In 2021 Helen Glover - twice Olympic champion in the women’s pair with Heather Stanning and three times a world champion - returned after a five-year absence, and as a mother of three, to win the European women’s pair title with Polly Swann.

They went on to finish an honourable fourth in the Tokyo 2020 Olympic final. 

"The reward is knowing that we crossed the line giving it our all," Glover commented. "The frustration would have been coming away from thinking we had more and we didn't."

Which offers evidence of a gold medal attitude to life…

For Gordie Howe, who quit ice hockey aged 43 in 1971 after one of the great careers, the lure of the ice proved too strong and, eight years later, he returned to the NHL for one more season, acquitting himself with honour as he scored 16 goals and provided 27 assists for the Hartford Whalers.

But the overwhelmingly most common story for those who seek former glories remains one of - relative - failure.

When Michael Schumacher retired in 2006, he had won a record seven world titles. Four years later, however, he returned to the circuit in search of an eighth. It never came, however - and in 2012 he left F1 for good.

A year before Schumacher’s first retirement another giant of his respective sport, United States cyclist Lance Armstrong, had called it a day after winning his seventh consecutive Tour de France.

That proud record would be entirely undone by subsequent doping revelations. But before that controversy came to a head as Armstrong returned to the sport in 2009. He never again won the Tour de France, however…

One reverse retirement in United States baseball caused some perplexity amongst the game’s observers - the recall of Satchel Page to the Atlanta Braves when the former acclaimed pitcher was…62 years old.

Segregation laws meant that Paige’s luminous talents were precluded from expression in Major League Baseball (MLB) until late in his career - he was 42 by the time he made his debut for the Cleveland Indians.

In 1968, almost ten years after he had last played, Paige made an appeal to all 20 MLB teams to sign him in order that he could achieve the 158 days of service required to qualify for the five-year minimum for his pension.

On August 12, the Atlanta Braves owner, William Bartholomay, agreed, employing Paige mostly as a coach but keeping him on the active roster, so one of the sport's greats was finally rewarded for his contributions to the game.