Final answer:
Larry Bird is the athlete who played 13 seasons for the Boston Celtics before coaching the Indiana Pacers.
Step-by-step explanation:
The athlete who played for thirteen seasons with the Boston Celtics and then served as head coach of the Indiana Pacers is Larry Bird. After an illustrious playing career with the Celtics, where he was recognized as one of the greatest basketball players of all time, Bird transitioned to coaching and led the Indiana Pacers. His impact on the game of basketball is significant both as a player and as a coach.