Frederick William was a German sovereign who ruled over the state of Mecklenburg-Strelitz as grand duke from 1860 until his death.

The Grand Duchy of Mecklenburg-Strelitz was a territory in Northern Germany, held by the younger line of the House of Mecklenburg residing in Neustrelitz. Like the neighbouring Grand Duchy of Mecklenburg-Schwerin, it was a sovereign member state of the German Confederation and became a federated state of the North German Confederation and finally of the German Empire upon the unification in 1871. After World War I and the German Revolution of 1918–19 it was succeeded by the Free State of Mecklenburg-Strelitz.