Novak Djokovic, from sick-note Serb to Grand Slam warrior

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.

Now, the 26-year-old world number one is the sport's greatest warrior whose steely Serbian eyes are firmly trained on a second Wimbledon title and seventh career Grand Slam trophy in his 11th final at a major.

His ability to thrive amongst the greats was never in doubt, but the size of his heart certainly was.

At Wimbledon in 2007, he retired with a back injury in the third set of his semi-final against Rafael 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 stamina anymore when he beat Rafael Nadal in the longest Grand Slam final of all time, a draining 5hr 53min marathon.

Another epic on Friday gave him a place in his second Wimbledon final, two years after he captured his only title at the All England Club.

His four hour 43 minute 7-5, 4-6, 7-6 (7/2), 6-7 (6/8), 6-3 win over Juan Martin del Potro was the longest Wimbledon semi-final in history.

Djokovic captured his first major 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, making him appear the rubber man of tennis.

Djokovic also refused to be resigned to the dominance of Roger Federer and Nadal who were carving up majors at will.

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 celebrate a calendar Grand Slam of all four majors.

Despite that, he still finished 2011 with a 70-6 win-loss record, a haul of 10 tournament victories and as year-end number one for the first time.

Back-to-back Australian Opens have followed in 2012 and 2013 although the French Open remains frustratingly out of reach.

Despite his success on the courts, and over $50 million in career earnings, Djokovic is wildly popular with fans for his strength of purpose on court and his offbeat sense of humour off it.

His Twitter account, which carries the tag-line, Laugh as long as you breathe, love as long as you live!, boasts over two million followers and he has developed a reputation for his sharp impressions of other players.

On the eve of Wimbledon at an exhibition event, Djokovic and Bulgarian star Grigor Dimitrov performed tongue-in-cheek impressions of Maria Sharapova's fussy on-court routine.

The crowd were won over, although Djokovic has had to curtail his impressions of other players in recent years with the likes of Roger Federer and the now retired Andy Roddick not amused by seeing themselves lampooned.

"I have tried all my life to be who I am. That's one of my mottos really, not pretending to be somebody else. I think that kind of character and strong position got me to where I am," said Djokovic.

"I did hold back (on the impressions) a little bit, because I think sometimes there is no time to really entertain that much.

"But I still feel that I am enjoying what I am doing, and I try to have fun wherever I go and as much as I can.

"Maybe tennis lacks that little bit of enthusiastic part of it, you know, entertainment, fun."