Daniel Gerard Marks II (November 19, 1909 - March 2, 1990) was an American Democratic politician best known for serving as a U.S. Senator for Florida from 1950, when he was appointed to replace his father, until his death in 1990, having served uninterrupted for forty years. In 1964, he ran as the Southern alternative to Joseph Kennedy, Jr. for the Democratic Presidential nomination, losing on the third ballot at the convention. On six different occasions he ran for Senate Majority Leader, and on all occasions he was defeated. He was a member of the prominent Marks family.