Professor William Francis Grimes (31 October 1905 – 25 December 1988) was a Welsh archaeologist who devoted his career to the archaeology of London and the prehistory of Wales. Born in Pembrokeshire, Wales, he received his education at the University of Wales. He held a number of prominent posts in Wales, including Chairman of the Royal Commission for Ancient Monuments in Wales. He published two influential volumes on the prehistory of Wales, with a particular interest in the Neolithic.
During the 1950s and 60s Grimes carried out dozens of excavations in the city of London in his capacity as director of both the Museum of London and the Institute of Archaeology, the institution within the University of London founded by Sir Mortimer Wheeler in 1937.
Grimes' most famous discovery was the London Mithraeum in 1954, a Roman temple to the god Mithras, uncovered during rebuilding work on a central London bomb site off Walbrook. Although the site was built over, Grimes succeeded in salvaging many of its finds and features including marble statuary attesting to the wealth of its congregation.
As a result of public pressure a replica temple was rebuilt elsewhere.