William VIII (10 March 1682 – 1 February 1760) ruled the German Landgraviate Hesse-Kassel from 1730 until his death, first as regent (1730–1751) and then as landgrave (1751–1760).

After his elder brother Frederick became King of Sweden in 1720 and his father died in 1730, he became de facto ruler of Hesse-Kassel.

He had a deep, personal friendship with Frederick the Great, King of Prussia, and Holy Roman Emperor Charles VII.

His second son and successor, Frederick, became a Catholic, which led to restrictions on Catholicism in the Calvinist landgraviate and the transfer of the Principality of Hanau to his Protestant grandson William.

During his reign, William started building Schloss Wilhelmsthal in Calden and collected paintings, including works by Rembrandt.