Boston Bruins Phil Esposito was the 1st NHL player to score 5 hat-tricks in one NHL season.

He scored his 3 goals (and 3 assists) vs Jack Norris & Denis DeJordy of Los Angeles Kings on January 14, 1971 at Boston Garden in a 9-5 Bruins win.

NOTE
Esposito would score 2 more hat-tricks before the season was over, finishing with 7 hat-tricks.
He scored 76 goals (152 pts) that season, the highest of his career.