William Sumio Naito (September 16, 1925 – May 8, 1996) was an American businessman, civic leader and philanthropist in Portland, Oregon, U.S. He was an enthusiastic advocate for investment in downtown Portland, both private and public, and is widely credited for helping to reverse a decline in the area in the 1970s through acquiring and renovating derelict or aging buildings and encouraging others to invest in downtown and the central city.