Cornelius Dennis "Mad Dog" Madigan (October 4, 1934 – January 2, 2024) was a Canadian professional ice hockey defenceman. He played 20 games in the National Hockey League with the St. Louis Blues during the 1972–73 season. The rest of his career, which lasted from 1955 to 1976, was spent in the minor leagues. Madigan was the oldest rookie in NHL history, aged 38.

Cornelius Dennis Madigan was born in Port Arthur, Ontario on October 4, 1934. After playing several years in senior leagues in Ontario and British Columbia in the late 1950s, Madigan had a lengthy career as a minor league star, most notably with the Fort Wayne Komets of the International Hockey League for three seasons in the early 1960s, and then for the Portland Buckaroos of the Western Hockey League for nine seasons. He won accolades as First Team league All-Star in 1960, 1966, 1967, 1968 and 1969, Second Team All-Star in 1965, 1971 and 1972, as well as winning best defenceman honors in 1966.

Beset with numerous injuries in the 1972–73 season, the St. Louis Blues of the NHL bought Madigan's rights from the Buckaroos, and he suited up for the Blues in January 1973 at the age of 38, becoming the oldest rookie ever. He played competently for the Blues in twenty regular-season games and five playoff games, before finishing his career with Portland in parts of the two successive seasons.^[1]

At the time of his retirement, Madigan was second in minor league history in career penalty minutes. A half century later, Madigan is still 77th in career penalty minutes.^[2]

In addition to Madigan's hockey career, he had a minor role in the 1977 cult classic movie Slap Shot as legendary hockey goon Ross "Mad Dog" Madison.^[3]

Madigan died in Portland on January 2, 2024, at the age of 89.^[4][5]