Died 1521AD

This Thomas O'Cathain, son of Aibhne, took over the chieftaincy of the O'Cathain Sept from his brother Sean O'Cathain. Thomas O'Cathain was a ruthless man and a parallel can be joined between his part in the murder of two sons of Sean O'Cathain, Godfrey and John Gallda by Walter McQuillan, at the instigation of Thomas. And the murders of the two young princes in the tower by Richard the third. The chieftaincy of Thomas O'cathain was to see the O'Cathain rip itself apart from internal strife, with brother maiming brother and cousin hanging cousin all in search for power and the title of "the O'Cathain". Thomas O'Cathain died 1521.