Dr. John Sumpter Bull (Ph.D) (born September 25, 1934) is a retired U.S. Navy test pilot and a former NASA astronaut.

Dr. Bull was a Navy fighter pilot with the VF-114 squadron aboard the carriers USS Ranger, USS Hancock, and USS Kitty Hawk. He graduated from the Naval Test Pilot School in February 1964 and was eventually selected as a member of the 'Original 19' astronaut selection group in 1966.

After briefly serving as a member of the Apollo 8 support crew as well as crew leader during vacuum-chamber Lunar Module testing, Dr. Bull resigned from the astronaut corps after learning that he was suffering from pulmonary disease. He attended Stanford University graduate school and received a Ph.D. in Aeronautical Engineering in 1973.

Dr. Bull returned to NASA and worked at the Ames Research Center from 1973 to 1985 where he conducted simulation and flight test research in advanced flight systems for both helicopters and fixed-wing aircraft. From 1986 until his retirement in 1989, he managed NASA wide research programs in autonomous systems technology for space applications.