John Leroy Hennessy (born September 22, 1952) is an American computer scientist, academician and businessman who serves as Chairman of Alphabet Inc.Hennessy is one of the founders of MIPS Computer Systems Inc. as well as Atheros and served as the tenth President of Stanford University. Hennessy announced that he would step down in the summer of 2016. He was succeeded as President by Marc Tessier-Lavigne. Marc Andreessen called him "the godfather of Silicon Valley."

Along with David Patterson, Hennessy was a recipient of the 2017 Turing Award for their work in developing the reduced instruction set computer (RISC) architecture, which is now used in 99% of new computer chips