O'Neil is a surname of Irish origin, often associated with various notable individuals and families. It can refer to historical figures, such as O'Neill chieftains in Ireland, who played significant roles in the country's history, particularly during the 16th and 17th centuries. In modern contexts, O'Neil may also refer to various places, businesses, or institutions, such as O'Neil Associates, a consulting firm, or O'Neil's Pub, a popular gathering spot. The name is prevalent in English-speaking countries and can be found in various forms, including O'Neal and O'Neill.