William Leeke (1797–1879) was a British Army officer and clergyman, known for his published reminiscences of the Waterloo Campaign, which form a primary source for many modern histories of the campaign.
Leeke was born in 1797 on the Isle of Wight to a naval family, who owned an estate in Hampshire. He was brother to Sir Henry John Leeke, who rose to the rank of admiral in the Royal Navy. Their father was Samuel Leeke, a deputy lieutenant of Hampshire, and their mother was Sophia, daughter of Capt. Richard Bargus, R.N. Leeke's eldest brother Samuel had also served in the navy, but died off Cadiz in 1810, while serving as a lieutenant. His sister, Urania, married Admiral Sir Edward Tucker.
William Leeke obtained his commission as an ensign in the 52nd (Oxfordshire) Regiment of Foot through the influence of Sir John Colborne (later Lord Seaton), the regiment's colonel, who was a relative: Leeke's mother's brother, Thomas Bargus, had married Colborne's mother. (Colborne's father had died in 1785, when he was seven). Originally joining the 52nd as a Gentleman Volunteer in May 1815, he was gazetted ensign almost immediately, the promotion dated 4 May. He was only 17, which made him the youngest ensign at Waterloo.
He carried the 52nd's Regimental colours during the Battle of Waterloo, which gave him a good understanding of the 52nd's actions during the battle.
Leeke purchased his promotion to lieutenant on 20 November 1823, and remained in the 52nd until 2 September 1824 when he exchanged into the 42nd Regiment of Foot, on half-pay. Despite the fact that he was by then studying at Cambridge, he returned to full-pay as a lieutenant in the Ceylon Regiment on 28 May 1828, by exchange. He sold out on 28 August 1828.