He played 16 seasons in the National Hockey League (NHL) with the St. Louis Blues, Calgary Flames, Pittsburgh Penguins and Boston Bruins between 1980 and 1997.

He was named the Central Hockey League (CHL) rookie of the year in 1980 and most valuable player in 1981 as a member of the Salt Lake Golden Eagles.

Born February 26, 1957, in New York City, Mullen grew up in the Hell's Kitchen neighborhood of Manhattan when it was controlled by Mickey Spillane (Last Gentleman Gangster).

[2] The boys' schoolyard games served as a partial inspiration for New York Rangers' general manager, Emile Francis, to create the Metropolitan Junior Hockey Association in 1966.

[1] Mullen did not learn to ice skate until he was ten years old, but at the age of 14 joined the Metropolitan association as one of the league's youngest players.

[3] Boston College offered Mullen a partial scholarship for the 1975–76 season to attend and play for the Eagles hockey program.

[12] Boston College has twice honored Mullen; He was inducted into the school's Varsity Club Hall of Fame in 1998, while the hockey program retired his jersey number 21 the following year.

[1] His small stature, coupled with a general bias against American players at the time, especially from non-traditional development areas, contributed to his failure to be selected.

[15] The Blues assigned Mullen to their Central Hockey League (CHL) affiliate, the Salt Lake Golden Eagles for the 1979–80 season.

[17] He missed the first three days of the Blues' training camp prior to the 1985–86 season in a contract dispute before agreeing to a one-year deal.

Mullen went to Calgary, along with Terry Johnson and Rik Wilson, for Eddy Beers, Charlie Bourgeois and Gino Cavallini.

[17] Mullen set a personal best of 47 goals in his first full year in Calgary, 1986–87, and with only 14 penalty minutes on the season, was voted the winner of the Lady Byng Memorial Trophy as the NHL's most gentlemanly player.

[1] He reached the 50 goal and 100 point milestones, leading the Flames with 51 and 110 respectively, and won his second Lady Byng Memorial Trophy.

[21] Though he played in his second All-Star Game in 1990,[23] Mullen's production fell by 41 points, to 69, and he failed to score at least 40 goals for the first time in six seasons.

[26] The move to Pittsburgh brought Mullen closer to his New York home and fulfilled his desire to raise his family in his native United States.

He missed the last two months of the regular season after having surgery to remove a herniated disc in his back,[27] an injury for which he could not identify a specific check or incident as the cause.

[5] Midway through the season, he became the first player in Penguins' history to have consecutive four-goal games, doing so against the New York Islanders on December 23, 1991, and the Toronto Maple Leafs three days later.

He added 6 points in 12 playoff games,[5] but the Penguins' attempt at a third consecutive championship ended with a Division Final loss to the New York Islanders.

[34] He missed the majority of the season after requiring surgery for another herniated disc,[35] then suffering a sprained medial collateral ligament.

[17] He appeared in eight games at the 1979 World Ice Hockey Championships, scoring seven goals and adding an assist for the seventh place Americans.

[40] At the age of 41, Mullen emerged from retirement to join the Americans for a qualifying tournament leading into the 1999 Men's World Ice Hockey Championships.

[44] "Mully spent a career excelling in areas of the ice a lot of guys wouldn't visit on a threat of death.

Mullen arrived in the NHL possessing great balance on his skates, an ability his teammates and coaches believed he gained from playing roller hockey.

[21] Penguins' play-by-play announcer Mike Lange nicknamed Mullen "Slippery Rock Joe" for his ability to evade opposing players.

Along with his brother Brian, Mullen was named a recipient of the Lester Patrick Award in 1995 in recognition of his contributions to hockey in the United States.

He was retained by the organization, however, and named interim head coach of the Wilkes-Barre/Scranton Penguins for the remainder of the American Hockey League (AHL) season.