Donald Kent Slayton (March 1, 1924 – June 13, 1993), better known as Deke Slayton, was an American World War II pilot, one of the original NASA Mercury Seven astronauts, and a NASA administrator.
After joining NASA, Slayton was selected to pilot the second U.S. manned orbital spaceflight, but was grounded in 1962 by a heart murmur. He then served as NASA's director of flight crew operations, making him responsible for crew assignments at NASA from November 1963 until March 1972. At that time he was granted medical clearance to fly, and was assigned as the docking module pilot of the 1975 Apollo-Soyuz Test Project, becoming the oldest person to fly in space at age 51. This record was surpassed in 1983 by 53 year old John Young and in 1998 by his fellow Project Mercury astronaut John Glenn, who at the age of 77 flew on space shuttle mission STS-95.