Jack Gilbert Hills (born 15 May 1943) is a theorist of stellar dynamics. He worked on the Oort cloud; the inner part of it, the Hills cloud, was named after him. He studied at the University of Kansas, where he was awarded an A.B. in 1966 and an M.A. in 1967. He was also awarded an M.S. by the University of Michigan, Ann Arbor. He spent much of his professional career at Los Alamos National Laboratory, which named him a Laboratory Fellow in 1998. Also the Hills mechanism in astrophysics is named after him. He proposed the mechanism in the 1980s.