I take a bit of a contrarian viewpoint on this.
I put these types of things into one of two buckets.
1 – New fans. I think most of the instances people will mention, a player may have drawn new attention to a sport, but those “new eyes” are less likely to last. This happens a lot at the collegiate level where spouses of fans start paying attention, fans of a school’s other sports start paying attention, etc. Typically, the effects are short-term while that player is playing and dissipates shortly after.
A smaller subset of this would be whole new fans to a sport. This is obviously the hardest to measure but I think you could point to several clear instances of it occurring at the different levels.
2 – Existing and casual fans. They are far more likely to have drawn attention from existing fans or casual fans that maintain or renew excitement and energy. I think most of the time, people that already pay attention to the sport tune in or pay attention, or sometimes renew/extend/maintain their attention.
I'd say those that had the biggest lasting impact would be Tiger Woods, Babe Ruth, Mickey Mantle, Hollyfield, Tyson, Jordan, Bird, Magic, Curry, Sheryl Swoopes, and Lisa Leslie. All are true generational talents.