One of the main responsibilities of a Brehon was to record the genealogies of the people. One of the most notable Brehons associated with recording genealogies was the Clan Mac Fhirbhisigh. Dubhaltach Mac Fhirbhisigh produced Leabhar na nGenealach, also the abridgment version Cuimre na nGenealach and Great Book of Lecan. The genealogist would also be referred to in old Irish as a Seanchaidhe. The basic family unit under brehon law in ancient Ireland was defined as Derbfine, or ‘True Kin’ in English Another Brehon family noted for recording genealogies were the Ó Cléirigh, such as Mícheál Ó Cléirigh, the author of the Annals of the Four Masters.