Here are 4 I came up with:
Charles O. Finley: owned those AWESOME Oakland Athletics teams in the 70s that won 3 straight World Series. No team other than the Yankees has ever done that. Had to give up ownership due to his divorce.
Ted Turner: bought the Braves and made them a consistent winner and essentially the center of the baseball universe. 14-straight division titles and a 1995 world championship.
John W. Galbreath: won 3 world championships as owner of the Pirates. Had the first all-black starting lineup in Major League history in 1971. Signed Roberto Clemente. Signed Dave Parker to the first million dollar contract.
Bill Veeck: owner of the Indians, Browns, and White Sox at various points. Broke the AL color barrier by signing Larry Doby, who would eventually lead Cleveland in their 111 win, World championship season in 1954.
This list is not exhaustive by any means. I am hoping you guys will chime in with additions so I can learn more.