William Ua Cellaig (modern Irish: Uilliam Buidhe Ó Cellaigh), also known as William Boy O'Kelly or William Buí Ó Ceallaigh, was Taoiseach of Uí Maine and Chief of the Name.
He died c.1381.
On Christmas Day, 1351, Ó Ceallaigh invited poets, artists, and writers from across Ireland to a feast in his home.
The feast became famous for the hospitality Ó Ceallaigh showed to his guests, and "Cuireadh fáilte Uí Cheallaigh romhainn" (literally: We got the O'Kelly welcome) remains a description for hospitable hosts in contemporary Irish.
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