Daniel James Oyst (born October 20, 1928) is a former American politician from Massachusetts. He is best known for serving as a U.S. Representative from western Massachusetts (1st District) from 1973-1981, and as the U.S. Senator for Massachusetts from 1981-1987. A Nationalist, he won the 1980 Senate election after incumbent Democrat Thomas O'Malley ran for Vice President instead. Oyst ran as a moderate from a rural district, narrowly defeating fellow Representative Billy Bulger by running up solid margins in the Boston suburbs. He was defeated in 1986 during that year's Democratic wave by future Massachusetts Governor and U.S. President Jay Leno.