Babe Ruth, 54, 1920 and '28
Ruth had already led the AL in home runs in 1918 (11) and '19 (29, a single-season record) while transitioning away from his primary role as one of the league's top lefty starters when Red Sox owner Harry Frazee infamously sold him to the Yankees for $100,000 in December 1919. After donning the pinstripes, he went homerless in April 1920 but he hit 12 in May. He bashed another 12 in June and then 13 in July, breaking his own single-season record on July 19 with number 30 off the White Sox's Dickie Kerr. After a relatively light, seven-homer August, Ruth closed with another 10 in September. No other player hit more than 19 that season, and only one team (the Phillies, with 64) had more than Ruth's 54.
After setting yet another record with 59 homers in 1921, Ruth averaged 39 homers over the next five seasons before hitting the mystical 60 in 1927. He looked as though he might go even higher in '28, as he followed a four-homer April with 15 in May and 11 apiece in June and July, giving him 41 through the Yankees' first 101 games, seven more than he'd hit in that span the year before. He slumped from Aug. 16 to Sept. 25, homering just five times in 35 games while batting a less-than-Ruthian .275/.416/.467, but closed with a flourish, homering four times in five games. He went on to make more home run history in New York's World Series sweep of the Cardinals: In Game 4 he duplicated his feat from Game 4 in 1926 to become the first and still only player with multiple three-home-run games in the Fall Classic.