Sir John Douglas Cockcroft, OM, KCB, CBE, FRS (27 May 1897 – 18 September 1967) was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus, and was instrumental in the development of nuclear power. From 1959 to 1967, he was the first Master of Churchill College, Cambridge. He was also chancellor of the Australian National University in Canberra from 1961 to 1965.