O'Toole, Brian (c.1525–1549), Gaelic warlord, was second of four sons of Toirdhealbhach (the elder) O'Toole (qv) (d. 1542), lord of the O'Tooles, and Sadhbh MacMurrough. Brian proved himself to be a powerful warlord and was known by his sobriquet ‘an Chogaidh’ (‘of the War’). It is likely that Brian an Chogaidh earned his reputation during his father's meteoric rise among the Irish of east Leinster (1535–42). Apparently Brian was not present on his father's last campaign of early 1542 to the Glen of Imaal against his rival and cousin, Toirdhealbhach mac Seaain O'Toole. As a result of Henry VIII's grant to him of the entire O'Toole lands in 1541, Toirdhealbhach the elder had gone to Imaal to exert more fully his legal rights over the territory of the recalcitrant O'Tooles of Imaal. Unfortunately for Toirdhealbhach the elder, he was killed in a devastating morning attack launched by Toirdhealbhach mac Seaain.
In the interregnum that followed, it was Brian's elder brother Toirdhealbhach Óg O'Toole (c.1520–1543) who emerged to succeed their slain father. Toirdhealbhach Óg, it seems, was determined to continue his father's plans to exert overlordship over the entire O'Toole possessions. This alarmed the lord deputy, Sir Anthony St Leger (qv) (d. 1559), who now switched his support to Toirdhealbhach mac Seaain, summoning him to the parliament of February and March 1542 at Limerick. But Henry VIII was determined that Toirdhealbhach the elder's heirs should receive his lands in their entirety. On 2 June 1542 St Leger and the Dublin council replied, claiming that Toirdhealbhach Óg, Brian an Chogaidh, and their brothers were illegitimate, delaying the issue of letters patent. In particular they pointed to the marriage of Toirdhealbhach the elder with Sadhbh MacMurrough, describing it as a mere hand-fastening. But the king would not brook St Leger's machinations, ordering him in July to issue letters patent to Toirdhealbhach Óg. In September the crown again showed its favour to Toirdhealbhach Óg, giving him a reward of £10. Inevitably Toirdhealbhach Óg, encouraged by the crown's favour, tried again to exert the rights of the senior O'Tooles over Imaal.
Toirdhealbhach Óg's efforts were to end in failure and in death, as Toirdhealbhach mac Seaain killed him sometime before May 1543. On 15 May St Leger and the Dublin council wrote to Henry VIII, informing him of the death. Now they asked that the lands of the deceased be made over to Brian an Chogaidh, describing him as ‘a right toward young man’. Brian, though, was shrewd enough to accommodate his younger brother Feilim O'Toole (qv) (d. 1603), sharing Powerscourt with him. But St Leger's change of position towards the family of Toirdhealbhach the elder was to reap immediate benefits in the coming years. While Brian an Chogaidh did not go, in 1544–5 some O'Byrnes and Art Óg O'Toole (qv) (d. c.1546) of Castlekevin campaigned for Henry VIII, most probably in Scotland.
The Dublin government placed further trust in Brian an Chogaidh during 1545, making him sheriff of Co. Dublin for that year. His service as sheriff was commendable, and earned him the praise of St Leger, who lauded him, saying: ‘this last yere one of the Tooles was shiref of the countie of Dublin, and executed the same right well, according to suche knowledge as he had’. In November 1546 he and his cousin Fiach mac Airt Oig O'Toole (qv) (d. 1578) of Castlekevin were rewarded for the services of their fathers, receiving grants confirming their inheritance. Brian an Chogaidh's grant included ‘all the lands which Tyrlaghe Otooll, his father, held of the king's gift’, holding them in tail male and through knight service.
In 1546 Brian an Chogaidh was to get yet another chance to prove his loyalty to the Dublin government, as a result of the revolt of Henry and Maurice an Fheadha Fitzgerald. Their revolt was probably prompted by the mysterious death of James Butler (qv) (d. 1546), 9th earl of Ormond, at a banquet in London during October. That event and the minority of Ormond's son, Thomas Butler (qv) (d. 1614), now 10th earl of Ormond, allowed the government a free hand to implement its policies in the midlands. Violence there was also fuelled and ignited by the resurgence of the activities of Fitzgerald dissidents among the O'Mores, O'Connor Falys, O'Tooles, and O'Byrnes in 1546–7. At some time during 1546 Henry and Maurice an Fheadha Fitzgerald, with the probable help of Toirdhealbhach mac Seaain O'Toole of Imaal, burned Rathvilly in Carlow as well as Rathangan and Ballymore in Kildare, but it is not clear whether these activities can be linked to the warring of Brian O'Connor Faly (qv) (d. c.1560) of Offaly and Giollapadraig O'More (d. 1549) of Leix or to the 1546 campaign of the lord justice, Sir William Brabazon (qv), against the Gabhal Raghnaill O'Byrnes of the central Wicklow highlands.
In Wicklow during 1547 there seem to have been at least two major outbursts of violence: in May, St Leger, perhaps aided by Brian an Chogaidh, defeated a renegade O'Byrne force and killed their leader, driving them into the mountain glens. Moreover, Brian must have been particularly pleased by the death of Toirdhealbhach mac Seaain O'Toole of Imaal, who was killed by the English about this time. But it was Brian himself who delivered the decisive blow to the Fitzgerald rebels. In the early summer he routed them at Three Castles near Blessington (the site of his father's victory in 1537 over John Kelway, constable of Rathmore), capturing Henry and Maurice Fitzgerald with fourteen supporters. These he conveyed to Dublin, where they paid a horrific price for their rebellion. For this last service Brian was rewarded in July with a lease of the rectory of Stagyonnll. However, he was to blot his record slightly, as evidenced by his pardon of 2 April 1549. But it counted for nothing, as he had died on 23 March 1549. He left two sons, but was succeeded by his younger brother, Feilim O'Toole.