Complex sentence: The prime author of the statues was Lionel of Antwerp, Duke of Clarence and by right of his wife-Elizabeth de Burgh, 4th Countess of Ulster-4th Earl of Ulster.
Split into simpler sentences: The prime author of the statues was Lionel of Antwerp, better known as the Duke of Clarence. He was also the 4th Earl of Ulster by right of his marriage to Elizabeth de Burgh, 4th Countess of Ulster.