The story behind the title - Earl of Tyrone - is quite complex and goes way back before the time of Sir Marcus Beresford. First holder was in fact Conn O'Neill, of the Tyrone O'Neills, who lived from 1480 to circa 1559. He had been granted the title by Henry VIII in 1542. Succeeding him in 1587 was Hugh O'Neill - Aodh Mór O'Neill - believed to be the illegitimate 2nd son of Conn's son, Matthew. However, he forfeited the title after the Flight of the Earls in 1607.
In 1673 the title was created once more, this time for Lord Power of Curraghmore, and became extinct in 1704 when the 3rd Earl passed away. It was once again created in 1746 for Marcus Beresford, 1st Viscount Tyrone, who was son-in-law of the last Power earl.