The NHL Calder Memorial Trophy is awarded annually to the most outstanding rookie player in the National Hockey League. Established in 1936, the trophy honors Frank Calder, the first president of the NHL. The winner is determined by a vote of the Professional Hockey Writers' Association at the end of the regular season. To be eligible for the Calder Trophy, a player must not have played more than 25 games in any previous NHL season and must be under 26 years old as of September 15 of the award year. This ensures that the award recognizes true rookie talent in the league.