I am not sure if you are talking only baseball but if not Oscar Robertson wore #1 at the end of his career when he was with The Milwaukee Bucks and teamed up with then Lou Alcindor to win an NBA Title in 1971, Alcindor's 2nd and Oscar's first in Milwaukee.
That season with Kareem and The Big O, The Bucks recorded a league best 66 and 16—the second-most wins in NBA history at the time, and still the most in franchise history to this day. During the regular season, the Bucks recorded a then-NBA record 20 game win streak. They then steamrolled through the playoffs with a dominating 12–2 record, winning the NBA Championship on April 30, 1971 by sweeping the Baltimore Bullets in four games.
With those numbers in mind I have to go with The Big O as the best ballplayer to ever wear #1 for a single season at least..He tailored his game to complement Kareem's extremely talented one to dominate the NBA.
wil.