Bolesław IV the Curly
Leszek of Masovia (, also "Lestek") (b. ca. 1162 - d. 1186) was a Polish prince from the Piast dynasty, the Duke of Masovia from 1173 until his death. He was the only son of Bolesław IV the Curly, Duke of Masovia and High Prince of Poland, to survive his father. After his father's death he inherited Masovia. At the beginning, Leszek ruled under the guardianship of his uncle Casimir II the Just. He was a man of poor health. For a short time he supported his other uncle, Mieszko III the Old, but later decided to reconcile with Casimir II, who after Leszek's death inherited his duchy.