Tomás Láidir Mac Coisdealbhaigh, Irish soldier and poet, fl.
Tomás Láidir Mac Coisdealbhaigh was a member of the Costello family of north Connacht who lost their lands in the Cromwellian confiscations of the 1650s.
Mac Coisdealbhaigh was in love with Úna Ní Dhiarmaida but her family refused to allow them to marry.
"He rode slowly and waited a long time in the ford itself, but finally on the mocking advice of his own servant, he crossed to the opposite bank.
Tomás killed the servant who gave him the evil counsel, and composed the famous song Úna Bhán."