Roger Federer "set the tone" for a new breed of tennis high achievers and his retirement brings time for reflection, his long-time rival Novak Djokovic said on Friday.
At the age of 41, battling knee trouble, Federer has decided to call it a day and intends to have a send-off on court at next week's Laver Cup.
Djokovic will join him on Team Europe for the match against Team World in London, with Rafael Nadal and Andy Murray also due to be involved.
An emotional finale to Federer's career is assured, in the city where he won eight Wimbledon men's singles title, just one of many records he established in a 24-year professional career.
Djokovic wrote on Instagram: "Roger it's hard to see this day and put into words all that we've shared in this sport together. Over a decade of incredible moments and battles to think back on.
"Your career has set the tone for what it means to achieve excellence and lead with integrity and poise. It's an honour to know you on and off court, and for many more years to come."
Djokovic holds a 27-23 head-to-head winning record against Federer, although their careers did not run precisely side by side, with Federer six years the Serbian's senior.
By the time Djokovic began to make a major impact on tour, Federer had arguably already hit his peak. From Wimbledon 2005 to the US Open in 2007, Federer reached 10 consecutive slam finals, a record that has not been matched.
He went past Pete Sampras' record of 14 majors in 2009, and Djokovic and Nadal have followed in his wake.
His longevity since has set a high standard for those two chief rivals, who have both recently edged ahead of Federer on the all-time list of men's grand slam singles title winners.
Federer won his 20th singles slam at the 2018 Australian Open, going closest to a 21st when he lost a thriller to Djokovic in the 2019 Wimbledon final, squandering two match points. Djokovic has 21, while Nadal leads the way with 22 titles.
Swiss great Federer retires with the most grand slam men's singles main draw wins in the Open Era (369), and as the only man to win 100-plus matches at two different slams (105 in Wimbledon and 102 at the Australian Open).
Addressing Federer, and pointing to his family, Djokovic added: "I know that this new chapter will hold amazing things for you, Mirka, the kids, all your loved ones, and Roger fans still have a lot to look forward to.
"From our family to yours, we wish you much joy, health, and prosperity in the future. Looking forward to celebrating your achievements and seeing you in London."