Born in Thunder Bay, Ontario, Gruen played junior with the local Vulcans of the TBJHL. He was chosen 58th overall by the Detroit Red Wings in 1972 and became a farmhand on the club for two years while receiving the occasional recall. In 1974-75, the young forward joined the Michigan Stags of the WHA and remained in the league for 2 1/2 seasons. His best performance came in 1975-76 when he scored 26 times for the Cleveland Crusaders.
After the Red Wings traded Gruen's rights to the Colorado Rockies in February, 1977, he returned to the NHL and recorded 18 points in 29 games. Following training camp the next season he was relegated to the Kansas City Red Wings of the CHL and remained in the minors for three years before retiring. Gruen returned to the game in 1982-83 with the senior Thunder Bay Twins. He registered 65 points in 36 games for the club before hanging up his skates for good.
Courtesy of the Hockey Hall of Fame