Rory O'More, also known as Rory Oge O'More (Irish: Ruairí Óg Ó Mórdha) (died 1578), was an Irish rebel.  He was the second son of Ruairí Ó Mórdha, captain of Leix, and Margaret, daughter of Thomas Butler, and granddaughter of Pierce or Piers Butler, eighth earl of Ormonde. Sir Henry Sidney once called him ‘an obscure and base varlet,’ but his family was one of the most important of the minor Irish septs, and also one of the most turbulent.

Rory Oge was a thorn in the side of the English during their attempts to seize lands from the Irish in the sixteenth century. In 1574, the authorities estimated they had spent £200,000 fighting and trying to capture O'More.  On New Year's Day 1577, a brutal massacre of the Irish gentry took place at Mullaghmast in Co. Kildare. Rory Og O'More vowed to avenge the deaths of his fellow countrymen. He kidnapped the relatives of important people. With the help of members from other clans, he destroyed large portions of Leinster and burned the town of Naas.

An observer noted, "Rori Oge O'More and Cormacke MackCormake O'Connor, accompanied with not more than 140 men and boys, on the third of the monethe burned between five and eight hundred thatched housies in a markett town called the Naas. They had not one horseman nor one shot with them. They ranne through the towne being open like haggs and furies of hell with flakes of fier fastened on pooles and so fiered the lowe thatched housies; and being a great windie night one house took fiere of another in a moment."

A reward of £1,000 was offered to anyone who could capture O'More. He was finally captured and killed in 1578. His head was displayed for all to see at Dublin Castle.