Mieszko III (c. 1122/25 – 13 March 1202), sometimes called Mieszko the Old, was Duke of Greater Poland from 1138 and High Duke of Poland, with interruptions, from 1173 until his death.
He was the fourth and second surviving son of Duke Bolesław III Wrymouth of Poland, by his second wife Salomea, daughter of the German count Henry of Berg-Schelklingen.
The last will and testament of the Piast duke Bolesław III Wrymouth of Poland, established rules for governance of the Polish kingdom by his four surviving sons after his death. By issuing it, Bolesław planned to guarantee that his heirs would not fight among themselves, and would preserve the unity of his lands under the Piast dynasty. However, soon after his death his sons fought each other, and Poland entered a period of fragmentation lasting about 200 years.
Leszek of Masovia (Polish: Leszek, 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.