Seven-times world champion Lewis Hamilton has led the tributes to Germany's Sebastian Vettel, who is retiring from Formula One at the end of the season.
Vettel won four world titles with Red Bull from 2010-13 but is quitting aged 35 following difficult stints at Ferrari and Aston Martin.
He is third on the all-time list of F1 race wins (53) behind Michael Schumacher (91) and Briton Hamilton (103).
"Seb, it's been an honour to call you a competitor and an ever greater honour to call you my friend," 37-year-old Hamilton, who ended Vettel's dominance by winning the first of six titles for Mercedes in 2014, wrote on Twitter on Thursday.
"Leaving this sport better than you found it is always the goal. I have no doubt that whatever comes next for you will be exciting, meaningful, and rewarding. Love you, man."
Current champion and standings leader Max Verstappen was effusive in his praise for Vettel.
"He has achieved so much in this sport that it's fully understandable for him to retire," the Dutch Red Bull driver told a news conference ahead of this weekend's Hungarian Grand Prix.
"Of course he's a great ambassador for the sport."
Haas driver Mick Schumacher, son of Michael, wished his fellow German well.
"I'm so sad that you're leaving, but at the same time excited for you and this new chapter of your life. You've been and still are such an important person to me and I'm thankful for our friendship," he tweeted.
"Thank you for everything you've contributed to the sport we both love, I can't wait for our last races together. Thank you, Seb - you're an inspiration."
