William Milligan (1821–1892) was a Scottish theologian.
William or Billy Milligan may also refer to: William Lane Milligan (1795–1851), British military surgeon William Milligan, Lord Milligan (1898–1975), Scottish politician and judge Billy Milligan (1955–2014), American multiple personality Billy Milligan (baseball) (1878–1928), American baseball player
ST1M (born 1986), Russian rapper also known as Billy Milligan