Captain William Martin Lays Siege to Grace O'Malley in Rockfleet Castle

William Óge Martyn (fl. 1566–1592) was the 101st Mayor of Galway.

Also known as William Óge Martyn fitz Thomas, he was a son of Thomas Óge Martyn and Evelina Lynch of Galway. Bailiff of Galway in 1566 to 1567, he was kidnapped by the Earl of Thomond in January 1570 but was free in time to participate at the battle of Shrule in April of the same year. He served as High Sheriff of County Galway and Jailer of Athlone Castle during the 1570s and 1580s.

Martyn attempted to capture or kill the pirate Grace O’Malley at her stronghold of Rockfleet Castle in 1579, but was repulsed.