Roger Federer said his return to world number one ranks among the best achievements in his record-breaking career.
The Swiss star became only the second man to lose the number one ranking and regain it when he beat Andy Murray in the ATP World Tour Finals on Tuesday night.
Federer lost the number one ranking he had held since February 2004 to Rafael Nadal after the Spaniard also claimed his Wimbledon crown in August last year.
Only Pete Sampras (number one for 1993-1998) has now been number one at the end of the season more times than Federer, while Czech-born Ivan Lendl is the only other man to regain his number one ranking.
"It means a lot to have returned to number one and to finish the year again at number one," Federer, who married his long-term girlfriend and celebrated the birth of twins this year, said.
"It was an incredible year for me both on the court and off the court and to be able to break the all-time grand slam record and finish the year on top is amazing."
Federer's year began in tears after Nadal beat him in the final of the Australian Open but he bounced back to win the French Open for the first time, albeit after Nadal was knocked out by Robin Soderling, and regained his Wimbledon title, although, again, Nadal did not participate.
That SW19 title was Federer's 15th grand slam, a record high in the game.
On Tuesday he confirmed his number one ranking with a 3-6 6-3 6-1 victory over Murray at the O2 Arena, where the world's eight best players are competing in the season-ending finale.