The name Ó Dochartaigh means "descendant of Dochartach". Dochartach was the 9th century legendary progenitor of the clann, whose name, meaning "hurtful", was likely given as a title of honor for his exploits in battle in the defense of his clansmen. While Ó Dochartaigh is anglicized as O'Doherty today, ancient genealogies and modern genetics indicate other Donegal families—the McDevitt or McDaid, the McMonigle, the McBride, and perhaps even others are also closely related or even at one time bore the Ó Dochartaigh name!

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Clann Ó Dochartaigh, known as an "ancient and valiant family", was one of the powerful Uí Néill dynasty, descended from Niall of the Nine Hostages, the semi-legendary 5th century high king of Ireland who captured the boy later known as Patrick on a raid. Our ancestor Conall Gulban, Nial's son, was the first Irish ruler to be baptized when St. Patrick later returned to Ireland. The descendants of Dochartach and likely those of his kinsmen, adopted the name Ó Dochartaigh within a number of generations, beginning one of the earliest existing hereditary surnames. During the medieval period, the Ó Dochartaighs assumed lordship over the territory of Kinel-Enda and Ardmire (roughly corresponding to the barony of Raphoe) in Donegal. Near the dawn of the 13th century two notable Ó Dochartaighs ruled as kings of all Donegal. Soon after this, the Ó Dochartaighs, increasing in both power and numbers, moved their power base northward, where the family ruled as lords of Inishowen over the surrounding tribes for a number of centuries. During this time a network of castles or keeps were built to defend the territory.

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