Ó Coileáin is an Irish surname meaning "descendant of Coileán", which itself comes from an Irish byname meaning "whelp, young dog." The name is historically tied to the Uí Chonaill Gabra, a medieval sept based in western County Limerick that served as the leading family of the larger Uí Fidgenti overkingdom, considered among the highest-ranked princes in Munster. Etymology and Variants The original Middle Irish form is Ua Cuiléin, which evolved into Modern Irish Ó Coileáin. The most common English forms are O'Collins and O'Cullane, while the surname Collins is also a variant. Additionally, Cullen may share a common origin. Historical Significance The Ó Coileáin family were kings of the Uí Chonaill Gabra sept, with records noting rulers such as Ó Cindfaeladh and Ó Cuilén in the 12th century. Following the Norman invasion of Ireland (late 12th century), a junior branch of the family migrated south, leading to the name becoming common in County Cork. Today, the surname is distributed across Ireland and its diaspora, primarily but not exclusively in Munster. Notable Bearers While the name is rooted in medieval Irish royalty, modern bearers include individuals in Ireland and abroad, though limited public records list well-known figures due to anglicization. The variants Collins and Cullen, however, have numerous notable bearers. Meaning: Descendant of Coileán Origin: Irish Type: Surname Usage: Ireland, particularly Limerick and Cork