Leszek, Duke of Masovia

Leszek of Masovia (Polish: Leszek Bolesławowic ) (c. 1162 – 1186) was the second Duke of Masovia and Kuyavia from 1173 until his death.

He was the second but only surviving son of Bolesław IV the Curly, High Duke of Poland by his first wife Viacheslava, daughter of St. Vsevolod, Prince of Novgorod and Pskov. Once it was thought that his mother was Maria, Bolesław IV's second wife, a fact which was shown in several web sources; however, after the discovery of coins where Leszek called himself son of Bolesław and Anastasia (the Greek or Latin equivalent of Viacheslava's name), this theory proved to be inaccurate. He was named either thanks to the courtly tradition preserved by Gallus Anonymus in his Cronicae Polonorum or after the eldest full-brother of his father, Leszek, who died young around 1131.

The death of his older brother Bolesław in 1172 left him as the only heir of his father. High Duke Bolesław IV (reportedly devastated by his first-born son's death) died one year later (3 April 1173), leaving Masovia and Kuyavia to Leszek, at the age of eleven or less. The overlordship of Poland (who included the control over Kraków and Gniezno), was taken by the eldest surviving brother of Bolesław IV, Mieszko III the Old.

Leszek began his rule under the guardianship of his youngest uncle, Casimir II the Just. According to the Bishop of Kraków and chronicler Wincenty Kadłubek, the young Duke of Masovia suffered of an extremely poor health and even after he formally took the government of his domains in 1177, the effective rule was handed by the magnate Żyron.

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