The first part of this review of Mac Giolla Phádraig Osraí history (1384-1534) covers the period 1384, from the conquest of Richard II, to 1454, by which time the clan had entered into an alliance with their mortal enemies, the Butlers of Ormond. Twelve years after the commencement of this era the Lordship of Ossory had fallen to Finghin Óg; these were days of increasing formation of alliances between Gaelic chieftains. That changed around the time of Finghin Óg s death in ca. 1417; the power struggle between Sir John Talbot and Sir James Butler, 4th Earl of Ormond, altered the face of Irish politics for the next 30 or so years, and Mac Giolla Phádraig Osraí had to choose one side or the other. It was a time when Donnchadh Mór, a previously unrecognised Lord of Ossory, was chieftain. His life and times are recounted from entries in the Annals of the Four Masters and other familiar texts, but three largely overlooked sources of Mac Giolla Phádraig Osraí history Liber Ruber, the Ormond Deeds and the Kildare Rental significantly add to our understand of both he and Mac Giolla Phádraig Osraí lineages, which to date have been muddled. New characters are uncovered, such as Morena ny Giolla Phádraig and her husband, John the Blind Butler, and the previously ignored branch, Clann Maeleachlainn Ruadh. An account of the early stages of the Ormond-Mac Giolla Phádraig Osraí alliance, which would ultimately fragment the clan, is provided.