Colmán was the son of Báetán mac Muirchertaig (died 572), also considered to be a high king, and belonged to the Cenél nEógain branch of the northern Uí Néill.
[2] His byname rímid means "the Counter", suggesting that he was numerate, unlike most contemporary kings.
[6] They are however omitted from the earliest king list, the Baile Chuind (The Ecstasy of Conn), a late 7th-century Irish poem.
In 602 Colmán defeated his Cenél Conaill rival, Conall Cú mac Áedo (died 604) at the Battle of Cúl Sleamna (in Raphoe barony) and Conall was put to flight.
[9] The Annals of Ulster state of this:[10]Of what value kingship, of what value law; of what value power over princes; Since it is king Colmán the Counter whom Lochan Dithnadha has slain?His daughter, or perhaps granddaughter, Fín, was the mother of Aldfrith son of Oswiu.