Mikołaj Sieniawski (c. 1489 – 1569) was a notable Polish magnate, military commander and a prominent politician of his times. He built Brzeżany Castle round which the modern town of Berezhany has developed. He is not to be confused with his descendant Mikołaj Hieronim Sieniawski, who was also a hetman in 1682 and 1683.