William de Brit, also known as William de Brett, was an Anglo-Norman Knight and Sheriff of Connacht until his death at the Battle of Ballyshannon in 1247.
References
Knox, Robert Thomas. The History of the County of Mayo to the Close of the Sixteenth Century. With illustrations and three maps. (Originally published c.1890. Castlebourke, De Burca 2000.
External links http://www.ucc.ie/celt/published/G100011/index.html