Short answers, pulled from the story.
Jerry Dior designed the Major League Baseball logo in 1968 while working for the marketing firm Sandgren and Murtha. His authorship was disputed for many years but was confirmed in November 2008 by ESPN writer Paul Lukas.
The MLB Batter logo was included on all on-field uniforms of Major League Baseball employees beginning in the 1969 season. It was introduced by Commissioner Bowie Kuhn to mark the 1869-1969 Professional Baseball Centennial Celebration.
The silhouette is not based on any specific player. Jerry Dior drew it with reference to photographs of several players, and the figure was chosen for its ambiguity so the batter could appear right- or left-handed and of any ethnic background.
In 2019, dark blue replaced royal blue in the logo's color scheme. The original palette, established in 1968, ran royal blue, white, and red from left to right.
The National Basketball Association, Minor League Baseball, Women's National Basketball Association, Arena Football League, U.S. Figure Skating, Hockey Canada, American Hockey League, PGA Tour, National Lacrosse League, Indy Racing League, and Major League Gaming have all used the same basic formula of a silhouetted athlete flanked by red and blue color blocks.
Jerry Dior created the MLB Batter logo in a single afternoon in 1968. Despite being completed so quickly, the design has remained essentially unchanged since it was adopted.