le Poer, Arnold (c.1280–1329), one of the foremost magnates of the lordship of Ireland in the early fourteenth century, appears to have come from one of the smaller branches of the le Poer family in Co. Kilkenny. He eventually became one of the two leaders of the fractured le Poer lineage, the other being John le Poer, lord of Dunoil (as shown when Arnold and John swore to discipline their family and followers before parliament in 1324). In 1310 he was accused of killing John Bonville, seneschal of Carlow and Kilkenny, and of being in league with the Gaelic lords of Leinster, but he was soon acquitted. Le Poer remained loyal to the king during the Bruce invasion and was present at the battle of Ardscull in 1316. His loyalty was rewarded by a grant of the manors of Oughterard and Castlewarden in Kildare on 17 May 1316. He also served as seneschal of the liberties of Carlow and Kilkenny and proved to be a loyal supporter of the king.
It was in his capacity of seneschal of Kilkenny that le Poer intervened in the proceedings against Alice Kyteler (qv) in 1324. He had developed close ties to Kyteler's son and was a kinsman of her fourth husband; he also appears to have let personal dislike of the bishop of Ossory, Richard Ledrede (qv), cloud his judgement and push him into an open feud with the bishop. One of his actions was to arrest Ledrede (April 1324), holding him till the day set for Kyteler's trial had passed; he also forcibly ejected the bishop from a session of the liberty court. The feud with Ledrede was patched over with a formal apology in the parliament of 1324, but within a year Ledrede was openly plotting against le Poer with the seneschal's other great enemy, Maurice fitz Thomas FitzGerald (qv), the future 1st earl of Desmond.
The dispute with fitz Thomas appears to have originated over control of the de Clare lordship of Thomond; this had been placed in the keeping of a John le Poer, but fitz Thomas had dispossessed him by 1320. At the root of the feud between the le Poers and fitz Thomas was the expansion of the Geraldine presence in Munster; but it was also compounded by the fact that le Poer was well regarded in England, while fitz Thomas was perennially out of favour at court. This situation did not change with the deposition of Edward II (January 1327), as le Poer was confirmed as seneschal of Kilkenny by the Mortimer regime. Later that year the dispute broke into open warfare, with the le Poers being supported by the de Burghs, and fitz Thomas by the Butlers and Ledrede. Both Arnold and John le Poer were trapped inside Waterford by fitz Thomas; Arnold le Poer fled to England, leaving his lands open to repeated raids by fitz Thomas. He returned to Ireland in the summer of 1328, possibly with William de Burgh (qv), 4th earl of Ulster, only to find that Ledrede had moved against him in his absence.
On 25 November 1328 Ledrede announced to the council in Dublin that he had tried le Poer for heresy and had convicted and excommunicated him. This left the justiciar, Roger Outlaw (qv), no choice but to arrest le Poer and confine him till the case could be heard by parliament in the session to be held in Dublin in January 1329. Outlaw himself was accused of heresy by Ledrede, acquitting himself with ease, but the charges against le Poer were held over till the next session (April). Unfortunately, le Poer died in prison (March) before the case could be heard. His death, coupled with that of his kinsman John le Poer of Dunoil six months earlier, removed the leadership of the le Poer family and also any opposition to fitz Thomas in Munster.