Irish personal naming system
A formal Irish-language personal name consists of a given name and a surname. Surnames in Irish are generally patronymic in etymology, although they are no longer literal patronyms, as Icelandic names are. The form of a surname varies according to whether its bearer is male or female, and in the case of a married woman, whether she chooses to adopt her husband's surname.
An alternative traditional naming convention consists of the first name followed by a double patronym, usually with the father and grandfather's names. This convention is not used for official purposes but is generalised in Gaeltachtaí or Irish-speaking areas, and also survives in some rural non-Gaeltacht areas. Sometimes the name of the mother or grandmother may be used instead of that of the father or grandfather.
Epithets
A first name may be modified by an adjective to distinguish its bearer from other people with the same name. Mór ("big") and Óg ("young") are used to distinguish father and son, like English junior and senior, but are placed between the given name and the surname: Seán Óg Ó Súilleabháin corresponds to "John O'Sullivan Jr." (although anglicised versions of the name often drop the "O'" from the name).