5 ... Harmon Killebrew, Babe Ruth, Hank Aaron, Barry Bonds, Alex Rodriguez.
122 different players have had a total of 295 40-HR seasons.
762 in 22 seasons and 9 post season home runs.
25 players
As many as the players can hit. There is no limit.
104
John Kruk hit 100 career home runs in 10 Major League seasons.
Cal Ripken Jr. has 431 career home runs in 21 Major League seasons.
Deion Sanders hit 39 career home runs in 9 Major League seasons.
Sammy Sosa (66,63) and Mark McGwire (70,65) during the 1998-1999 seasons.
If you are talking two separate seasons then it is A-Rod.
25
As of 2009, 125 players have hit 300 or more career homer runs in the Major leagues..