William Barclay Foster (1779 - 1855) was the father of Stephen Foster, a well-known American songwriter. William was an important businessman in his time. Some people have written about him and have called him one of the most prosperous merchants of Pittsburgh, Pennsylvania. He worked in the state of Pennsylvania as a state legislator. He was also elected mayor of Allegheny City two times. (Allegheny City is now part of the city of Pittsburgh.) He married Eliza Clayland Tomlinson on November 14, 1807, in Chambersburg, Pennsylvania.