Daniel O'Neill united in his person the two main branches of a great family. His father, Con, son of Niall, son of Brian Fagartach O'Neill, was lord of Upper Clandeboy; his mother Ellis (a sister of Eoghan Ruadh) belonged to the O'Neills of Tyrone. Daniel was born in Clandeboy early in the seventeenth century. His father died while he was a minor, and he was brought up a protestant, and, it is stated, a ward in chancery in England. He served his apprenticeship to arms with the English regiments in the Netherlands, and at an early age became familiar with the life both of camp and court. He was endowed with many natural advantages: a pleasing appearance and engaging manners, great fertility of resource, and an aptitude for handling difficult men and situations with a finesse which earned for him the name of ‘Infallible Subtle’.