Peter Mackenzie Millman was a Canadian astronomer. He worked at the Dunlap Observatory from 1933 until 1940. In early 1941 he enlisted with the Royal Canadian Air Force. In 1946 he joined the Dominion Observatory in Ottawa. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.