Roger Federer became the oldest ATP world number one when he beat Robin Haase to reach the semi-finals of the ABN AMRO World Tennis event in Rotterdam on Friday.
Here are some facts about Federer and his ranking.
First time reached number one: 2004
Age when first reached number one: 22
* Federer holds the record of 302 weeks as world number one. American Pete Sampras managed 286.
* Federer, 36, is now the oldest player to reach the top of the rankings. American Andre Agassi did it aged 33 in 2003.
* Federer is the oldest man or woman to be number one. Serena Williams was 35 when she relinquished top spot in the women's rankings in May.
* By returning to number one for the first time since Nov 2012, Federer has set a new record for the longest gap between separate stints in the position.
* He also sets a new record for the longest time between first topping the rankings and the latest spell there. Rafael Nadal did hold that record after reclaiming top spot last August, having first scaled the summit in 2008.
* Federer's 237 continuous weeks at world number one from 2004 to 2008 is also a record.
Other facts about Federer
* Since Federer was number one in 2012, Novak Djokovic, Rafael Nadal and Andy Murray have held the top spot.
* Federer had a five-year grand slam drought, ending it by winning the 2017 Australian Open to reach 18 majors.
* In winning this year's Australian Open he took his tally to 20, and has won three of the last five slams.
* Federer has been year-end world number one five times, one behind the record of Sampras.
* Only seven other players who were in the top 100 when Federer first got to number one are still in there now: Nadal, Tomas Berdych, Richard Gasquet, Feliciano Lopez, David Ferrer, Ivo Karlovic and Mikhail Youzhny.