Arms of O'Brien: Quarterly of 4: 1&4: Gules, three lions passant guardant in pale per pale or and argent (O'Brien); 2nd: Or, (perhaps argent), three piles conjoined in point gules; 3rd: Or, a pheon azure (Sydney?)
Percy Wyndham-O'Brien, 1st Earl of Thomond (c. 1713 – 1774) was a British Member of Parliament and an Irish peer.
When Percy was 28 years old in 1741, Henry O'Brien, 8th Earl of Thomond died without issue and in his will left all his Irish estates to him as the younger son of his wife's sister. In compliance with the terms of the bequest, Percy took the additional surname name of O'Brien.[2] On 11 December 1756,[3] he was created Earl of Thomond and Baron Ibracken (the second creation).