Crimthann Cualann (d. 633), son of Áed Dibchíne and overking of Leinster, belonged to the dynasty of Uí Máil. His sobriquet associates him with Cualu, the Bray area in north Wicklow. He had at least six brothers, including Toca king of Cualu, and Rónán who was apparently a bishop. The Leinster king-list assigns Crimthann a reign of twenty-eight years, although his predecessor in the provincial kingship, Rónán son of Colmán, who probably belonged to the dynasty of Uí Chennselaig, died only in 624. Presumably, therefore, this reckoning combines an earlier reign as king of Uí Máil.
Crimthann was not a strong king, and apparently posed little threat to the rising power of Uí Dúnlainge and its Uí Néill allies; these concentrated most of their energies at this time against Uí Chennselaig and its ruler Crundmáel Bolc Luatha. Nonetheless, it is possible that the pillaging of Leinster by the new Uí Néill overking Domnall (qv) son of Áed (qv) in 628 was directed against Crimthann. When the potential threat of Uí Chennselaig had been reduced, Crimthann was attacked by a combination of the Uí Dúnlainge dynast Fáelán (qv) son of Colmán, Fáilbe Flann (qv) king of Cashel, and Conall Guthbind, Uí Néill king of Uisnech. These allies defeated and slew Crimthann in 633 (637, Ann. Inisf.) at the battle of Áth Goan, in the west of the Liffey plain, probably in Kildare. Crimthann left at least three sons, Fiachra, Aillil, and Óengus; a certain Tuathal may well have been a fourth son. The kingship of Uí Máil was continued in the line of his brother Rónán the bishop, whose descendants included Fiannamail (qv) and Cellach Cualann (qv), both overkings of Leinster.