Final answer:
Mario Lemieux is the three-time Art Ross Trophy winner who scored back-to-back 56 goals in successive seasons, an achievement that contributed to his winning of the trophy awarded to the NHL's leading scorer.
Step-by-step explanation:
The three-time Art Ross Trophy winner who had back-to-back 56 goals is Mario Lemieux. The Art Ross Trophy is awarded to the National Hockey League (NHL) player who leads the league in scoring points at the end of the regular season. This prestigious award recognizes the talent and skill of the league's top scorer.
Mario Lemieux won the Art Ross Trophy for the 1987-1988, 1988-1989, and 1995-1996 seasons, showcasing his outstanding ability to score and assist, thereby accumulating a high number of points. His consistent performance, particularly the achievement of back-to-back 56 goals in successive seasons, has cemented his legacy as one of the sport's most gifted offensive players.