Who developed the "Gretzky Rule" in hockey?

The "Gretzky Rule" was indeed developed by the NHL Board of Governors. This rule relates to the salary cap structure in the league and was implemented to prevent teams from excessively financially rewarding a single player, particularly referencing Wayne Gretzky's legacy and impact on the game. The rule surfaced in response to the uniquely high salaries players began to demand and the potential for imbalance that created within the league.

The other entities mentioned do have diverse roles in hockey but don’t relate directly to the creation of rules governing league salary structures. The International Ice Hockey Federation focuses on international competitions and regulations. The Hockey Hall of Fame serves primarily to honor players, builders, and officials in the sport, without direct implications on game rules. The Players' Association represents players' interests but does not enact rules; it collaborates with the league's governing bodies to negotiate terms surrounding gameplay and player contracts. Thus, the NHL Board of Governors is the correct source for the development of the "Gretzky Rule."