Albert Einstein did not specifically express his opinion about Pierre de Fermat, the renowned French mathematician. Fermat, who lived in the 17th century, made significant contributions to various areas of mathematics, including number theory and calculus. He is particularly famous for his Last Theorem, which he wrote in the margin of a book but claimed to have found a proof that was too large to fit in the margin. This theorem remained unproven until 1994 when mathematician Andrew Wiles finally provided a proof.
While Einstein is well-known for his contributions to physics and his groundbreaking theories, his writings and documented opinions do not extensively cover specific historical mathematicians or their work. Thus, there is no widely known or documented opinion of Einstein regarding Fermat. It is worth noting that Einstein had a great appreciation for mathematics and recognized its importance in the development of his own theories, but his focus was primarily on physics and the nature of the universe.