David "Dave" Thomas (born May 20, 1949) is a Canadian comedian and actor. He was born in St. Catharines, Ontario, but moved to Durham, North Carolina where his father, John E. Thomas, attended Duke University and earned a PhD in Philosophy. Thomas attended George Watts and Moorehead elementary schools. The family moved back to Dundas, Ontario in 1961 where he attended Dundas District high school and later, graduated with an honours Bachelor of Arts degree in English Literature from McMaster University in Hamilton, Ontario. Thomas was granted an honorary doctorate from McMaster University November 20, 2009.

He is the eldest son of John and Moreen Thomas. John E. Thomas (1926–1996) was a noted medical ethicist, head of the Philosophy Department at McMaster University, and the author of several books. Moreen Thomas was a church organist for 30 years and noted composer of church music. He is the older brother of Canadian singer-songwriter Ian Thomas. Thomas is married and has four children. His sons, Johnathan Thomas and Harrison Thomas are members of the Los Angeles heavy metal group Tinhorn, with whom Thomas appeared on Tom Green Live. Thomas has two daughters: Emily and Charlie.

Starting his career as a copywriter at ad agency McCann Erickson in 1974, he became the head writer of the Coca-Cola account in Canada within a year. After watching a Second City stage show in Toronto, and while suffering from self-proclaimed "boredom" in his advertising work, he auditioned for the Second City troupe and was chosen as a performer.