What is the last name of the American actor Kirk, who is the father of the actor Michael?

Explanation

Michael Douglas is an American actor and producer. He often plays controlling, successfull, all-knowing businessmen or political characters. He was in films such as 'The Jewel of the Nile' (1985), 'Wallstreet' (1987), 'Basic Instinct' (1992), 'The Game' (1997), 'Traffic' (2000) and 'Wallstreet II' (2010). Michael Douglas is married to Catherine Zeta-Jones and is the son of the great actor Kirk Douglas.