Mononen, a member of the Finnish Hall of Fame, was considered a trailblazer for his country when he signed a professional contract with the Phoenix Roadrunners in the World Hockey Association.

He had earlier made his national debut aged 18 when scoring a hat-trick against Poland.

He scored two goals and seven points in nine games at the 1969 World Championships in Stockholm. 

This was followed by more success at the 1972 Winter Olympic Games in Sapporo, where he finished second on the goal scoring charts behind the Soviet Union's Valeri Kharlamov.

Mononen’s Finnish record for most points scored in a World Championship, 15, set the same year in Prague, stood until 1999 when Saku Koivu notched 16 points in Lillehammer.

He spent two seasons in North America before time in the Finnish and Swiss leagues.

Mononen represented Finland in six World Championships, one Olympics and one Under-18 European Championship.

His induction into the Finnish Hockey Hall of Fame took place in 1991.