William IV of Saint Omer (1155-1191) was Castellan of Saint Omer from 1171 to 1191, succeeding William III of Saint Omer and preceding William V of Saint Omer.
Biography[]
William of Saint Omer was born in Saint-Omer, Kingdom of France in 1155, the son of William III of Saint Omer. He succeeded his father as Castellan of Saint-Omer in 1171, and he married the sister of James of Avesnes and fathered William V, William VI, and Nicholas I. William later emigrated to the Kingdom of Jerusalem and became the lord of Haifa, Le Destroit, and Caymont in the Holy Land. He died in Palestine in 1191.