The surname O'Clery, derived from the Gaelic Ó Cléirigh, is historically documented as the oldest recorded surname in Ireland, tracing its origins back to approximately 920 CE in modern-day County Galway. The name originates from the word cléireach, which translates to clerk or clergyman, indicating that the early bearers of this distinguished lineage were often learned scribes, scholars, or religious figures. Over subsequent centuries, as hereditary surnames became institutionalized across Gaelic society, the name evolved and spread, eventually giving rise to widespread anglicized variants like Clarke while retaining its profound historical roots in Irish genealogy.