Donnchad Máel Na Mbó (d. 1006), son of Diarmait and king of Uí Chennselaig, belonged to the lineage of Síl nOnchon. He played an important part in retaining the Uí Chennselaig kingship for that segment of Síl nOnchon that later emerged as the family line of Mac Murchada. He was usually referred to by his sobriquet Máel na mBó (devotee of the cattle), which may reflect his accumulation of cattle tributes. His father, Diarmait son of Domnall, had taken the kingship after the death of his cousin Bruatar son of Echtigern (981). It appears that some modus vivendi was reached between the rival lines, as Áed son of Echtigern (Bruatar's brother) died as tánaise (heir-apparent) of Uí Chennselaig in 993. Máel na mBó married Aífe, daughter of Gilla-Pátraic king of Osraige. They had at least two sons, Domnall Remur (qv) and Diarmait (qv) (d. 1072), who was generally referred to as Mac (son of) Máel na mBó.
Máel na mBó acceded to the kingship of Uí Chennselaig probably soon after the death of his father (997), although the king-list in the Book of Leinster – in some disarray at this point – omits mention of him and of several of his successors. Before long, Máel na mBó was faced with renewed conflict within the lineage of Síl nOnchon. In 1003 he slew one of his leading rivals – Áed, the rígdamna (one eligible for the kingship), apparently a son of the tánaise (heir-apparent) Áed son of Echtigern, who had died ten years earlier. The breach of sanctuary involved in slaying his rival in the oratory of Ferns is noted with disapproval by the annalists. Máel na mBó was himself slain (1006) ‘by his own kinsmen’; it seems clear that he was still quite a young man. Although his killers are not expressly identified, it is probable that they were members of Áed's family.
There was evident confusion in the Uí Chennselaig regnal succession following his death; for a time north Leinster interests were successful in intruding rulers of the Uí Muiredaig lineage, Máel-mórda (qv) son of Lorcán and his kinsman Tadc. Máel na mBó's sons, Domnall Remur and more particularly Diarmait, came to prominence in the 1030s; the latter, who achieved an extensive overkingship, was the ancestor of all the later kings of Leinster.