William Stanley, 6th Earl of Derby, KG was an English nobleman. Stanley inherited a prominent social position that was both dangerous and unstable, as his mother was heir to Queen Elizabeth I under the Third Succession Act, a position inherited in 1596 by his deceased brother's oldest daughter, Anne, two years after William had inherited the Earldom from his brother. After a period of European travel in his youth, a long legal battle eventually consolidated his social position. Nevertheless, he was careful to remain circumspect in national politics, devoting himself to administration and cultural projects, including playwriting.
Following the resolution of the succession dispute between the daughters of Ferdinando, Earl of Derby and their uncle, William, Earl of Derby, it was ruled that the daughters of Ferdinando were the rightful heirs to the title of Lord of Mann. As the oldest of them would not reach the age of majority until 1609, two temporary Lords of Mann were appointed by James I, using letters patent, so that the daughters could benefit from the Island's revenues.
Following the coming of age of the heirs to the Lordship of the Isle of Man, the rights over the island were sold to their uncle, William Stanley, 6th Earl of Derby. He took up the title of Lord of Mann following the passing of an Act of Parliament.
While retaining the title of Lord of Mann, Derby passed the administration of the Isle of Man to his niece, Anne Stanley. In 1612 he transferred the title to his wife, Elizabeth.