He was the half - brother of Brian O'Neill , Cormac MacBaron O'Neill and Hugh O'Neill , Earl of Tyrone .
Art MacBaron O'Neill was part of the O'Neill dynasty of Ulster , the illegitimate son of Matthew O'Neill , 1st Baron Dungannon .
Art MacBaron O'Neill was the O'Neill     of Brian O'Neill , Cormac MacBaron O'Neill and Hugh O'Neill , Earl of Tyrone .
Art MacBaron O'Neill was part of the O'Neill dynasty of Ulster , the illegitimate son of Matthew O'Neill , 1st Baron Dungannon .