Died 1522AD

This Donnell O'Cathain, son of Sean O'Cathain, late chieftain of the O'Cathain, was never chieftain of the O'Cathains. Nicknamed "the Cleric" possibly because he had been educated for the church, he was accompanied in latin, but his behaviour was anything but clerical. In 1503 he maimed his own brother Richard, this was not an unusual happening in tridal affairs for only someone physically fit could succeed to the office of chief, and potential rivals were at times removed from the running in this way. This deed was followed by Donnell's murder of his own nephew, Manus son of Brian Finn in 1506.

With Thomas O'Cathain growing old, the obvious contenders for the title of "the O'Cathain" were his nephews, firstly Donnell the Cleric and Donough. Donnell career continued in a ruthless fashion with the hanging of Alexander MacQuillan in coleraine in 1513, the following year finds the O'Donnells beseigning Donnell's castle at Coleraine. Resulting in the O'Donnells demolishing it in revenge for Donnell the Cleric violation of guarentee given to the O'Donnells. Donnell the Cleric apparently lived in Coleraine, as he is described as "of Coleraine" in the funeral entry of a grandson, Cowy Ballagh O'Cathain. The next five years saw Donnell the Cleric locked in a bitter fued over the succession to the chieftaincy. In 1522 Donnell the Cleric, "the paragon of the youth of the tribe, and a man of general hospitality," was killed by the people of the Route.

Unfortunately for the O'Cathain Sept, the death of Donnell the Cleric would result in a even more bitter succession dispute between the relatives of Donnell, ripping the Sept apart at a time when external enemies where closing in on the territory of the Sept.

A fitting lesson in the life of Donnell the Cleric would be:

"Then said Jesus unto him, Put up again why sword into his place: for all they that take the the sword shall perish with the sword". Matthew Ch26 V.52