This isn’t about being the greatest. It’s about being a game changer. Here are mine in no particular order ...
Jackie Robinson - integrated the country’s most popular sport
Babe Ruth - the first genuine power hitter
Julius Irving - first above the rim star
Dirk Nowitzki - first big man who could play all five positions
Bobby Orr - first player who completely controlled puck play
Sammy Baugh - QB who changed how football was played
Deacon Jones - defined pass rushing
Mohammed Ali - boxing style, persona and social conscious
Arnold Palmer - Arnie’s Army put golf on the map
Dick Fosbury - revolutionized how the high jump was done
Two I thought of but I couldn’t get into the ten are Billie Jean King and Serena Williams. King put women’s tennis on the map. Williams is the first brute force female player.