William VIII ruled the German Landgraviate Hesse-Kassel from 1730 until his death, first as regent (1730–1751) and then as landgrave (1751–1760). Born in Kassel, he was the seventh son of Charles I, Landgrave of Hesse-Kassel and Maria Amalia of Courland. After his elder brother Frederick became King of Sweden in 1720 and his father died in 1730, William became de facto ruler of Hesse-Kassel. He officially became landgrave after his brother's death on 25 March 1751. In 1736 Johann Reinhard III of Hanau-Lichtenberg, the last of the Counts of Hanau, died. Those parts of his county belonging to the County of Hanau-Münzenberg, which included Hanau, were inherited by the Landgrave of Hesse-Kassel.
At the end of the 16th century, Count Philipp Ludwig II (1576-1612) had attracted Protestant refugees from the Netherlands and France to found their own settlement, or New Town, south of Hanau. These Walloons brought high-class trade, their knowledge of jewellery and the production of other luxury items and, therefore, taxes to the county. William further encouraged this migration and offered privileges and financial incentives to anyone who was willing to set up in business in Hanau. French speaking Hugenot jewellers were attracted to the city and within a very short period of time, Hanau had developed into an important center for luxury goods with some thirty-two bijoutiers involved in the production of gold boxes alone. An enthusiastic art collector, William built Schloss Wilhelmsthal in Calden and used it to house his collection of paintings, including works by Rembrandt and Johann Heinrich Tischbein the Elder. Each room in the princely appartments was individually decorated with Rococo painted and gilded rocaille panelling, plasterwork and rich silk hangings, and furnished with the finest Rococo furniture, all conceived in relation to each other - the carving found on the chairs and sofas matching the stuccoes in what is now called the ‘Frederician Rococo’. The interiors of Wilhemstahl and its furniture are largely intact today, and undoubtedly one of the most prized items in the collection is the ‘Peacock feather commode’, dated circa 1755, and applied with mother-of-pearl plaques combined with painted peacock feathers on silver foil in shades of blue and green. The collection also includes numerous Chinese and Japanese porcelains from different eras. The 1926 inventory of the Schloss reveals that William was purchasing snuff-boxes from the Parisian goldsmith Girost & Compagnie in 1752, see F. Bleibaum, Schloß Wilhelmstal: Die Bau- und Kunstdenkmäler im Regierungsbezirk Cassel…, Kassel, 1926, pp. 15 and 132. William was a close personal friend of Frederick The Great of Prussia (1712-1786), himself the owner of one of the most important and finest collections of snuff-boxes to have ever been assembled.