Admiral of the Fleet Sir William Parker, 1st Baronet, GCB, was a Royal Navy officer. As a captain's servant he took part in the Battle of The Glorious First of June in June 1794 during the French Revolutionary Wars and, as a captain, he participated in the capture of the French ships Marengo and Belle Poule at the action of 13 March 1806 during the Napoleonic Wars. He was detached on an independent command on the Tagus in September 1831 with a mission to protect British interests during the Portuguese Civil War. As Commander-in-chief of the East Indies and China Station, he provided naval support at various actions between 1841 and 1842 during the First Opium War. Appointed Commander-in-Chief, Mediterranean Fleet in February 1845, he was briefly First Naval Lord in the First Russell ministry from 13 July 1846 to 24 July 1846 but gave up the role due to ill health before returning to his command with the Mediterranean Fleet.

Admiral of the Fleet is a five-star naval officer rank and the highest rank of the Royal Navy, formally established in 1688. The five-star NATO rank code is OF-10, equivalent to a field marshal in the British Army or a Marshal of the Royal Air Force. Apart from honorary appointments, no new admirals of the fleet have been named since 1995, and no honorary appointments have been made since 2014.