Even Rod Laver, arguably the only challenger now to Roger Federer's ever-growing status as the greatest men's tennis player of all time, says he is "in awe" of the Swiss marvel.
At Wimbledon to celebrate the 50th year of his 1969 calendar-year grand slam sweep, Laver has offered a fascinating insight into not only Federer's legendary feats on the court, but also the ageless champion's remarkable human spirit off it.
"Even now I get a thrill every time I see him out on the court," Laver told an intimate gathering of Australian tennis greats and their families and friends.
"He's always a perfect gentleman on the court. He competes hard ... I mean, I'm in awe of him, I really am."
Laver, now 80 and still the only man in the 50-year professional era to win all four grand slam titles in the same year, was being interviewed by former world No.1 John Newcombe at a barbecue held in his honour when the conversation diverted to Federer.
"We're both reasonably quiet individuals," Laver noted.
"But the nice thing about Roger, I guess, was the first time that we sort of really knew each other was when I presented him with the Australian (Open) trophy when he had won it (in 2006).
"He felt like what was I doing out there presenting a trophy, and so he got emotional (and cried)."
A decade on and Laver said Federer's decision to initiate a new teams' event, pitting Europe against the World and name it in the Australian's honour was testament to his class as a person.
"The Laver Cup, that all started with Roger," he said.
"Roger felt tennis has been here now 50 years, for open tennis, but he says 'way before that, there's so many great champions, whether it be Perry, Vines, Riggs.
"All the way down the line to 'Emmo' (Roy Emerson) and Hoad, Rosewall and he says 'everybody's going to forget there was a tennis game for the amateurs'.
"He said 'let's try and have something and we'd like to use your name as a throwback to all the amateur players in that era'.
"So it's wonderful to see Roger play and compete.
"But, for me, it's better because I just know him."
Newcombe, the long-time host of the traditional Aussie Wimbledon barbecue, recalled another tale about Federer that also revealed a lesser-known side to the 20-times grand slam champion.
Newcombe was walking into Melbourne Park before the 2017 Australian Open final, in which Federer, at 35 and on the road back from a career-threatening knee injury, famously beat Rafael Nadal to claim his 18th slam having not played a tournament in the six months beforehand.
Newcombe remembered peering through the glass of the players' restaurant an hour before the final, and seeing Federer and Laver sitting together "with nobody else around".
"They're just chatting and I'd seen Rocket (Laver) but I hadn't seen Roger," Newcombe said.
"So I just walked into the dressing room to say good luck to Roger and I said: 'What, is Rod giving you some last-minute tips on how to play left-handers?'
"Roger said 'No, actually we're discussing about dinner' - and both of them are just completely relaxed and it's an hour before the match.
"I said: 'What's with the dinner?'
"Roger said: 'Well, at Indian Wells, they auctioned off for people to have dinner with Rod and myself and we haven't been able to arrange it so we're talking about a date to try to get together with this person who bought it at auction.'
"I said: 'Wow, I bet that got something reasonable for the dinner - 30 or 40 thousand?'
"And Roger said: 'No, as a matter of fact, four hundred thousand, and half of the money goes to my charity in Africa for the children, which is fantastic - but the best part of it is I get to have dinner with Rod Laver.'
"Totally relaxed, an hour later, he goes out and wins this unbelievable five-setter against Rafa."
After winning another titanic tussle with Nadal on Friday (Saturday AEST), Federer will face world No.1 and defending champion Novak Djokovic on Sunday hoping to land an unprecedented ninth Wimbledon men's singles crown.
And, fittingly, Rod Laver will be in the Royal Box to see it.