Sir William Beatty was an Irish surgeon who served in the Royal Navy. Born in Derry, Ireland, he joined as a surgeon's mate in 1791 at the age of 18. He is best known as the ship's surgeon aboard HMS Victory during the Battle of Trafalgar, at which he witnessed the death of Admiral Horatio Nelson, and for writing an account of that battle – Authentic Narrative of the Death of Lord Nelson.

The Battle of Trafalgar was a naval engagement that took place on 21 October 1805 between the British Royal Navy and the combined fleets of the French and Spanish Navies during the War of the Third Coalition of the Napoleonic Wars (1803–1815).