Novak Djokovic was once the sick-note Serb whose undoubted promise was at the mercy of a variety of frustrating aches, pains and assorted strains.
But with a third US Open title to go with the Wimbledon crown he secured in July he has matched American Pete Sampras on 14 Grand Slam titles and there is little doubt that the 31-year-old is one of the sport's greats.
Djokovic, playing in his eighth US Open final, delivered a businesslike 6-3, 7-6 (7/4), 6-3 victory over third-seeded Juan Martin del Potro of Argentina.
Since a quarter-final exit at Roland Garros left him threatening to skip Wimbledon, he has lost just one match, claiming not only a third title at the All-England Club but also a first Cincinnati Masters title in the build-up to the US Open.
From his lowest ranking in 12 years, he continues to rise. Sixth coming into the Open he is projected to rise to three in the world.
Now, Djokovic is three behind Rafael Nadal's total of 17 Slams, six shy of Roger Federer's record of 20.
But he has time on his side -- Federer has already celebrated his 37th birthday.
"Of course he can," said Del Potro when asked if Djokovic can claim the record over Federer.
"He has 14 already. He won two Grand Slams in one year. He's healthy. He has a great team working with him.
"Novak has everything to make records in this sport."
Djokovic's ability to thrive amongst the greats has never been in doubt, but the size of his heart led to questions in his early days.
At Wimbledon in 2007, he retired with a back injury in the third set of his semi-final against Nadal.
He also quit at the 2006 and 2007 French Opens at the third round and quarter-final stages respectively, while at the 2009 Australian Open, where he was defending champion, he pulled out of his quarter-final with Andy Roddick citing heat exhaustion.
But at the 2012 Australian Open, nobody was questioning his courage anymore when he beat Nadal in the longest Grand Slam final of all time, a draining 5hr 53min masterpiece.
Djokovic captured the first of his 12 majors in Melbourne in 2008, but it was three years before he added his second.
He dropped gluten from his diet, his lithe physique allowing him to chase down lost causes, transforming him into the rubber man of tennis.
After leading Serbia to a maiden Davis Cup in 2010, he raced through the first half of 2011, building up a 48-1 winning run.
Only a semi-final defeat at the French Open prevented him from becoming just the third man to capture a calendar Grand Slam.
Despite that, he still finished 2011 with a 70-6 win-loss record, a haul of 10 tournament victories and year-end number one for the first time.
- People's champion? -
Back-to-back Australian Opens followed in 2012 and 2013, although the French Open remained frustratingly out of reach with three heart-breaking losses until his 2016 breakthrough.
In Paris that year, he became the first player to break through the $100 million barrier in prize money.
Djokovic has also not been afraid to innovate, bringing in Boris Becker as part of his coaching team for the start of the 2014 season.
He then became a vegetarian.
Off court, Djokovic married long-time girlfriend Jelena Ristic in July 2014.
They have two children, a son Stefan and daughter Tara.
However, despite his achievements, Djokovic appears doomed never to be held in the same esteem as Federer and Nadal, the 'people's champions'.
There are those that see something a little more calculating in the Djokovic make-up, a player prone to affectation.
In the 2015 French Open semi-finals, he was castigated for taking an eight-minute medical time-out after dropping the third set against Andy Murray.
At Indian Wells in 2016, he was roundly criticised for his comments on equal prize money for women.
Even at Wimbledon this year, he criticised some Centre Court fans for lacking respect towards him while schedulers exiled him to Court Two for his third round match.