Ulick Fitzrickard De Burgh

According to the Book of the Burkes (Historia et Genealogia Familiae de Burgo), a genealogical manuscript made in the 1570s for Seaán mac Oliver Bourke, 17th Mac William Íochtar (d.1580) of the Burkes of County Mayo, Burke was a son of Richard an Fhorbhair mac William de Burgh, a natural son of William Laith de Burgh (d.1324), who was a son of Richard Óg de Burgh, illegitimate son of William de Burgh (d.1206) original founder of the de Burgh/Burke dynasty in Ireland. The same descent is given by Duald MacFirbis in his Leabhar na nGenealach (Book of the Genealogies), mostly compiled in 1649-50, and its revised abridgement the Cuimre na nGenealach (Binding of the Genealogies) of 1666. This is the ancestry presented by John O'Hart in his Irish pedigrees; or, The origin and stem of the Irish nation (1876), and in the Oxford A New History of Ireland (1984), where the authors write "The origins of the Clanricard line are not absolutely proven, but the descent given is that in the best Irish genealogical sources and is not contradicted by contemporary sources."

On this view, Burke would have been the leader of an illegitimate branch of the de Burgh family that were already strong in south Connaught, and were able to use the conflict of the 1330s to establish themselves as an independent lordship. The name "Clanricarde", first recorded in 1335, would reflect their ancestry from Richard Óg de Burgh, and might have already been in informal use for a number of generations.

However, as noted by Martin J. Blake in 1911, the pedigree above is not without its problems. In particular, William Liath de Burgh, the founder of the Franciscan Abbey in Galway, is known to have died in 1324. As Blake writes "it is obvious, having regard to these dates, that he could hardly have been a grandson (as these writers represent him to be) of the first William de Burgh in Ireland, who died early in A.D. 1206 as the English State Records prove." The MacFirbis pedigree also omits Burke's successor, Richard Óg Burke, 2nd Clanricarde (d.1387) whose existence is well attested. Blake concludes that MacFirbis and the earlier manuscript "are accurate as regards the genealogy they give of the Mac William Bourkes of Mayo (Mac William Eighter) but that they had no accurate information regarding the early part of the pedigree of the Mac William Burkes of Clan-Ricard (Mac William Oughter) and could only make a guess at it–with the not surprising result, that they made a mess of it."

A different ancestry for Burke was given by John Lodge in his Peerage of Ireland (2nd ed, 1789),[5] and followed by Edmund Lodge in his Genealogy of the Existing British Peerage (1832).==