This is what a golden human looks like.

On Sunday night, Roger Federer won his sixth Australian Open, defeating Croatian Marin Cilic at Rod Laver Arena in five sets.

36 years of age. 20 Grand Slam titles. Still winning five-set battles.@rogerfederer beats Marin Cilic 6-2, 6-7(5), 6-3, 3-6, 6-1 to win the @AustralianOpen ???? pic.twitter.com/wsX0yol98R

— Wimbledon (@Wimbledon) January 28, 2018

But it’s his behaviour off-court that has attracted the most attention during his time in Australia.

When his ultimate challenger Rafael Nadal was forced to bow out after an injury, Federer wrote to him.

“I wrote Rafa late last night before I went to bed,” he said at a bursting Rod Laver Arena, having beaten 19th seed Tomas Berdych in straight sets in the Australian Open quarterfinal moments before.

“Last thing I did. I said I have to write Rafa to see how he’s doing. I hoped he was going to be OK with the scan today.”

“I’m hoping the news was not terrible,” Federer told interviewer Jim Courier. “It was not nice to see a fellow rival and friend like this go out. I wish him well.”

It wasn’t the first time the 36-year-old has sent a handwritten note to a competitor.

The Swiss man has made writing to his fallen rivals a habit since at least 2004, when former world no. 4 James Blake slammed into a net post while practicing on a clay court in Rome.

I got one note from a player in the hospital when I broke my neck. @rogerfederer Tennis is lucky to have such an amazing ambassador for the game. https://t.co/wfCogHivwJ

— James Blake (@JRBlake) January 24, 2018

It wasn’t a tweet. It was a handwritten note from the #1 player in the world. Just something many players wouldn’t take time out of their day to do for a fellow competitor in the middle of a tournament.

— James Blake (@JRBlake) January 24, 2018

It’s just one of the many things that make the father-of-four admired and adored in unrelenting abundance. Since going professional in 1998, Federer is credited with invoking the Golden Age of the game; since he won his first grand slam crowd sizes and television ratings have exploded into another stratosphere. Between 2004 and today, Federer and his counterparts in Nadal, Novak Djokovic and Andy Murray have seen prize money at grand slam tournaments almost triple.

Arriving at a time of inflated egos and racket-smashing outbursts, he was the floppy-haired antidote to the International Tennis Federation’s attitude migraine.

His special magic is difficult to distill.

Federer never shouts. He never insults the umpire. He never boasts about his millions or throws jabs at his opponents. He’s never photographed leaving somewhere he shouldn’t be. He never delivers a grouchy press conference. He never points the finger at his box when he double faults. Hell, he doesn’t even look like he’s tired after playing five sets.

Listen: Are young tennis players really brats, or is their behaviour a subtle cry for help? Jessie Stephens argues in their defence, on Mamamia Out Loud.

Federer’s freakish talent explains why millions clamber to see him perform (novelist David Foster Wallace once wrote that watching him play was akin to a religious experience) but it’s his personality – that humbleness, cheeky wit and kindness – that makes spectators hang on his every word post-match.

Not a single seat is vacated until Federer has spoken.

When he lost the 2014 Wimbledon title to Djokovic in a monster five-set epic, he told the crowd:

Winning or losing, it’s always something special and something you’ll remember, even more so when the match was as dramatic as it was today. It’s even more memorable when I see my kids there with my wife and everything. That’s what touched me the most, to be quite honest. The disappointment of the match itself went pretty quickly.

It’s this side to Federer – Federer the husband of Mirka and the dad of Myla, Charlene, Leo and Lenny – that makes the whole world swoon.

Only he could go decades in the sport uninjured before tearing his meniscus in 2016 in his own home. While running a bath for his twin daughters, he heard a click. He realised something was awry when they were walking around the zoo that afternoon.

It's just so goddamn simple and winsome - like everything Federer does. And that's before you take into account the millions of dollars his Roger Federer Foundation has raised for disadvantaged children and victims of natural disaster.

In the 20 years he has been an athlete, Roger Federer hasn't just mastered his craft, he has epitomised what sportsmanship looks and sounds like.

"He's a golden human," my mum said while we watched his interview last night. "He's just utterly golden."

And I think that's perhaps the best way to describe it.