Federer finally won the French Open after three times finishing runner-up
Pete Sampras hailed Roger Federer as the best player of all time after the Swiss matched his record of 14 Grand Slam titles at the French Open.
Federer beat Robin Soderling 6-1 7-6 (7-1) 6-4 to win his first Paris title.
"What he's done over the past five years has never, ever been done - and probably will never, ever happen again," said Sampras.
"Regardless if he won there or not, he goes down as the greatest ever. This just confirms it."
Federer joins Fred Perry, Don Budge, Roy Emerson, Rod Laver and Andre Agassi as the only men to have won all four Grand Slam titles.
The 27-year-old, who lost to Rafael Nadal in the last three French Open finals, was presented with the Coupe des Mousquetaires by Agassi.
The Las Vegan, who won eight Grand Slam titles in his 20-year career, says Federer's statistics are unmatched.
"We're watching two guys in the prime of their years compete against each other - and Nadal has an answer for Federer. But what criteria do you use to judge best ever?" stated Agassi.
"Roger's numbers - it's hard to disagree with. His domination on different surfaces - hard to disagree with."
Sampras won 14 Grand Slam titles but never made it past the semi-finals at Roland Garros.
The American is convinced that Federer has not only surpassed his own achievements but those of Australian Rod Laver, who twice won all four Grand Slams in the same year.
"Now that he's won in Paris, I think it just more solidifies his place in history as the greatest player that played the game, in my opinion," he added.
"I'm a huge Laver fan and he had a few years in there where he didn't have an opportunity to win majors. But you can't compare the eras and in this era the competition is much more fierce than Rod's."
Laver completed the coveted Grand Slam for the first time in 1961, but he turned professional in 1962 and was banned from competing in the major tournaments until the open era began in 1968.
He won his second Grand Slam in 1969, although three of the four tournaments were then played on grass.
The Australian, now 70, says it is impossible to compare players from different eras but he told BBC Radio 5 Live: "Federer is the greatest player in his era.
Federer is the greatest - Rusedski
"He's a great champion and a credit to the game with the way he competes on and off the court."
Federer, who matched Ivan Lendl's record in reaching his 19th Grand Slam final, believes he should be judged when his career is over.
"I don't know if we'll ever know who was the greatest of all time but I'm definitely happy to be right up there," said Federer, who plans to play into his 30s.
"I think it should be judged at the very end. I don't know. It's for other people to decide."
After a tense five-set win over Juan Martin del Potro in Friday's semi-final, Federer outclassed surprise finalist Soderling on Sunday.
"He's a great player," conceded the beaten Swede.
"He doesn't have any weaknesses at all. He really deserves to be called the best player of all time."
Former British number one Tim Henman, who played against both Federer and Sampras in their prime, also believes Federer has the edge.
"What puts Federer ahead is that his game is complete," Henman told BBC Sport.
"Sampras was a phenomenal player and his record speaks for itself but you always felt there were aspects of his game that you could target.
"Winning in Paris just emphasises that Federer is the ultimate all-court player."