Some people are calling Novak Djokovic, who just won his sixth Wimbledon title and his 20th Grand Slam singles title, the greatest tennis player of all time. Is it possible to realistically compare great players (or teams) in any sport, for that matter, with those of prior eras?

Yes.

(Unless you treat it as a life or death matter)

Yes, but never forget the greatest accomplishments of prior or other champions, they all deserve our respect.

Yes, and Djokovik is not the greatest.

Federer is possibly the greatest ever, followed by McEnroe, Laver, Borg and Connors.

Yes.

But context is necessary in the fact of technology, better medicine, improved condtioning and training, and the huge amount of finance through advertising and sponsorship.

Just talking tennis, but different eras have different levels of competition on the various surfaces, different racquet tech, and different physical requirements. Any tennis player who is second best ever on clay is not going win many French Opens and appear weak on clay if he/she coincides with the best ever player on clay. Conversely the third best ever may have an easy run and win every year.

If Grand Slam titles are the yardstick, then I'd say there is a three-way tie for GOAT at the moment. However, I feel that titles are just one way to measure. There are other things such as rivals, impact on the game, etc.

As far as comparing across eras, it is a fun exercise and good for bar talk, but ultimately pointless. I agree with kyushubill above - context is needed. Is Serena Williams the GOAT? What if Steffi Graff had not retired at 30? What is Martina Navratilova had Serena's training and equipment? What if Serena had to play with wooden and cat-gut rackets? What if hand-checking was illegal in Michael Jordan's day like it is now? What is Mark Spitz used today's swimsuits? Babe Ruth never had to travel further west than Chicago and south than DC in his day. What if he had to go east coast to west coast and then to Florida and Texas like today's players? Like I said, good fun, but pointless.

This is such a difficult question to answer because players faced other players of differing levels at different times of their careers, techniques and equipment were different, illnesses and injuries have put an end to some careers. I prefer the Greatest Players of All Time, not one particular. For the women's I would choose, in no particular order, Navratilova, Graf and Williams. For the men's, the current Big Three, although Federer had little challenge early in his career. Once the other two matured, he struggled. But there's no denying, there's only one GOAT on clay.

What if Steffi Graff had not retired at 30? What is Martina Navratilova had Serena's training and equipment?

What if Monica Seles had not been stabbed by that demented fan (why is he still alive, anyway?)

Personally, I prefer the question of what was the greatest rivalry in tennis? I witnessed just Federer-Nadal_Djokovic and Sampras-Agassi to date, and of course McEnroe-Bjorg is famous. Lendl, Becker, Edberg, I don't really know. I prefer these rivalries that lead to insane battles, rather then a dominant player who crushes all opponents.

And if you just like statistics, the title leaders after 1990.

https://en.wikipedia.org/wiki/List_of_ATP_Tour_Top-level_tournament_singles_champions

Yes, although in many cases context needs to be added to show the differences in rules between previous champs and current ones, as well as advances in technology that may have assisted. And, as one poster said, we should also never forget previous greats.

He surely is currently the greatest. Former great players were of course also outstanding in their era, but probably wouldn’t even make it into qualification for nowadays’ tournaments.

I don't think that a player who has behavior issues on the court should ever be called the greatest player of all times. A great player is not solely judged by his wins but also by his behavior on court. Thumping his chest like a primate, ripping of his shirt, hitting a linesmen with a ball, smashing his racquet on court and the list goes on. For me Federer and Nadal would be the greatest players of all times and Djokovic comes in as a player who still needs to grow up and mature before he can even come into consideration. Daniil Medvedev was graceful in calling him that but for me, Daniil is a greater player than Djokovic because he behaves like one. Even in the match with Medvedev, Djokovic showed his immature behavior by smashing his racquet to bits. I don't think Head is pleased with that little performance and without sponsors, Djokovic would be back in Serbia and not living in splendor in Monaco.