Ó Leannáin is an Irish Gaelic surname, representing a variant form of Lennon. The name originates from the Gaelic byname Leannán, meaning "lover" or "paramour". This byname was used to describe a person characterized by love or affection, eventually becoming a hereditary surname passed down through generations in Ireland. Historically, Ó Leannáin is one of several anglicized variants of the original Irish Ó Leannáin, which was prevalent in certain regions, particularly in County Galway and surroundings. The prefix “Ó” denotes “descendant of,” indicating lineage from a notable ancestor named Leannán. Over time, spellings shifted; anglicized forms such as Lannon appeared as English speakers adapted the Gaelic phonetics. The parent name Lennon rose to international prominence in the 20th century due to John Lennon (1940–1980), a founding member of The Beatles and a renowned musician and peace activist. While Lennon himself was of Irish descent, his surname traces back to Ó Leannáin ancestors. The fame of John Lennon contributed to Lennon’s adoption as a given name, and at the same time brought visibility to its Gaelic root, including variants such as Ó Leannáin. In modern usage, Ó Leannáin remains a relatively rare surname, more common in genealogical records than in contemporary populations. It often appeals to those researching Irish heritage, as the spelling retains a clear connection to the original Gaelic form. Genealogy websites like Forebears show limited distribution, underscoring its heritage as a culturally significant rather than purely widespread name. While Ó Leannáin is rarely encountered outside of Ireland and areas of significant Irish diaspora, its connection to both ancient Irish onomastics and a globally famous figure makes it a name of lasting interest.