Y-DNA analysis of Fitzpatricks has turned traditional historical narratives of how the surname was taken on its head. The attachment of the surname Fitzpatrick to the Barons of Upper Ossory, who were supposedly the descendants of Mac Giolla Phádraig Osraí and, in turn, of an ancient Laighin (Leinster) lineage, is no longer sustainable. DNA insights and critical assessment of historical records have demonstrated that those who claim to descend from the barons have a Y-haplotype consistent with them emerging from a line of clerics out of a Norman-Irish origin ca. 1200 AD. Questions arise, therefore, regarding the origins of other large Fitzpatrick groups who, based on Y-DNA, can be shown to descend from ancient Irish. Could any of these lines descend from the Mac Giolla Phádraig Osraí of old, those of Annalistic fame? For the first time, this article introduces the Mac Giolla Phádraig Dál gCais in a scholarly narrative. Mac Giolla Phádraig Dál gCais are, unquestionably, an ancient Pátraic surname clan. But are they also a Mac Giolla Phádraig lineage that arose in Osraí in ancient times? Such a question radically disrupts traditional narratives, yet the answer is ‘maybe’ – sound historical, genealogical, and name occurrence evidence supports the view that there is no need to adhere to a singular patrimony for the Mac Giolla Phádraig Osraí and that a Dál gCais line was well positioned to have territory in Osraí and adopt Mac Giolla Phádraig as a surname. With certainty, the Mac Giolla Phádraig who are the subject of this article are Dál gCais on a genetic basis since, via their paternal haplotype, they share common ancestry with Brian Bóruma, High King of Ireland. The descendants of those Mac Giolla Phádraig Dál gCais feature through ancient records for An Clár (Clare) are still found in the County, yet many derive from lines that were dispersed from their ancient An Clár homelands in the seventeenth-century. From An Clár to Oileáin Árann (Arann Islands), and Gaillimh (Galway), and – one way or another – on to Maigh Eo (Mayo), and Ros Comáin (Roscommon), they are a great and ancient Mac Giolla Phádraig Clan, who at times held much wealth, power, and influence. And some were smugglers!