You could argue until the end of time about who is the greatest tennis player in history.
Maybe you would opt for Martina Navratilova, surely the most revolutionary figure in the women's game; or Steffi Graf, the only player to have achieved a Golden Slam comprising all four major singles titles and Olympic gold in a calendar year; then there's Margaret Court, still the record-holder when it comes to grand slam singles victories.
Perhaps Roger Federer or Rafael Nadal – two present-day icons who will renew their glorious rivalry on Sunday – get your vote? Or the great Rod Laver? Some could make a case for Novak Djokovic, particularly if he was to go past Federer's record haul of 17 slams. There are other names worthy of mention.
However, after victory over elder sister Venus in the Australian Open final saw her move clear of Graf as the winner of the most singles titles in the Open Era, Serena Williams' claim to be the greatest of all time is undoubtedly a strong one.
And there is one aspect of her success that is particularly admirable: her ability to dominate at an age when most players are some way past their best.
Federer, of course, has been rightly feted this week for reaching the final in Melbourne at the age of 35, no mean feat for a player who has recently been sidelined for six months.
Yet while the Swiss would be worthy of the highest praise should he beat old rival Nadal on Rod Laver Arena to improve his record haul of men's singles titles to 18, he has understandably found it tougher to contend for slams in recent years, with the younger Djokovic establishing himself as the main man on the ATP Tour.
Consider, also, the three women who sit alongside Williams as the most prolific women's singles champions.
Navratilova's peak came between 1982 and 1987, when she won at least two slams each year and 14 of the 18 she racked up in total.
Her penultimate slam singles success at the 1987 US Open came just before she turned 31, with one further title secured at Wimbledon three years later.
Graf, who won every major honour in 1988 and claimed three slams in four subsequent years, only secured one after her 28th birthday, the 1999 French Open, while Court's last three slams were all earned in the year the Australian turned 31.
In contrast to that trio, Williams has been able to enjoy her most sustained period of success in her 30s – a fact made even more impressive by the troubles she faced after winning Wimbledon for the fourth time in 2010.
A freak foot injury, sustained when the American stepped on broken glass leaving a restaurant in Munich, and the more serious matter of a pulmonary embolism prevented Williams from featuring in the next three slams and she played just six tournaments in 2011.
However, since she reclaimed the Wimbledon title in 2012, Williams has won half of the 18 subsequent majors – aided by a second 'Serena Slam' of four in a row completed with yet another triumph at SW19 two years ago.
It could be argued that the present era is a relatively weak one when it comes to women's tennis. Venus, now 36, and Maria Sharapova – currently serving a suspension – are the only recent opponents of Serena with more than two slam crowns to their name.
While Federer has been forced to play second fiddle at the back-end of his career to the likes of Djokovic and Andy Murray, Serena has been the clear number-one scalp in her field for some time – even at points when she has slipped from the top of the WTA rankings.
Yet when a Twitter user raised that topic on Saturday, stating: "Serena is a great champion, no question about it, but she's never had a serious rival....," Chris Evert – Navratilova's great adversary – replied: "But that's not her fault! [She] played at a higher level!"
Regardless of how highly you rate her competitors, Williams is certainly breaking new ground by remaining the player to beat in her 36th year.
The greatest of all time? Quite possibly. But who is to say Williams is anywhere near finished?