Thomas William Heinsohn was an American professional basketball player, coach, and broadcaster. He was associated with the Boston Celtics of the National Basketball Association (NBA) for six decades as a player, coach and broadcaster. He played for the Celtics from 1956 to 1965, and also coached the team from 1969 to 1978. He spent over 30 years as the color commentator for the Celtics' local broadcasts alongside play-by-play commentator Mike Gorman. He is regarded as one of the most iconic Celtics figures in the franchise's history, known during his lifetime for his charisma and loyalty to the team and its traditions. From this, he earned the nickname "Mr. Celtic".

The Boston Celtics are an American professional basketball team based in Boston. The Celtics compete in the National Basketball Association (NBA) as a member of the Atlantic Division of the Eastern Conference. Founded in 1946 as one of the league's original eight teams, the Celtics play their home games at TD Garden, which is also the home of the National Hockey League's Boston Bruins. The Celtics are regarded as one of the most successful teams in NBA history and are tied with the Los Angeles Lakers for the most NBA championships with 17. The Celtics currently hold the record for the most recorded wins of any NBA team.