Roger Federer became the oldest world No. 1 in ATP history in 2018. He reclaimed the top ranking on 19 February 2018 after reaching the Rotterdam Open semifinals, doing so at 36 years and 320 days old.
The achievement followed Federer’s victory at the 2018 Australian Open, where he defeated Marin Cilic in five sets to win his 20th Grand Slam singles title. He then accepted a wildcard into Rotterdam and won the matches needed to guarantee his return to No. 1.
Federer surpassed Andre Agassi’s previous record for oldest ATP world No. 1 by more than three years. His return was especially notable because he had not held the ranking since November 2012; the gap between his periods at No. 1 lasted five years and 106 days.
The record was later surpassed by Novak Djokovic, but 2018 remains the year Federer set it. Federer also became the player with the longest span between his first and most recent dates at No. 1.