990 – 10/11 May 1034) is King of Poland during 1025–1031, and Duke from 1032 until his death.
He wis the second son of Bolesław I the Brave, but the eldest born from his third wife Emmilda, daughter of Dobromir, possible ruler of Lusatia.
He was probably named after his paternal grandfather, Mieszko I.
His second name, Lambert, sometimes erroneously considered to be a nickname, was given to him as a reference to the cult of Saint Lambert.
Also, it is probable that this name Lambert was chosen after Bolesław I's half-brother Lambert.
It is thought that the choice of this name for his son was an expression of warming relations between Bolesław I and his stepmother Oda.
He organizes two devastating invasions to Saxony in 1028 and 1030.
Then Mieszko II runs a defensive war against Germany, Bohemia and the Kievan princes.
Mieszko II is forced to escape from the country in 1031 after an attack of Yaroslav I the Wise, who installs Mieszko's older half-brother Bezprym onto the Polish throne.
Mieszko takes refuge in Bohemia, where he is imprisoned by the Duke Oldrich.
In 1032 he regains power in one of the three districts, then unites the country, making good use of the remaining power structures.
At this time, several Polish territorial acquisitions of his father are lost: Upper Lusatia (also known as Milsko), part of Lower Lusatia, Red Ruthenia, western and central part of Upper Hungary (now Slovakia) and probably Moravia.
Mieszko II is very well educated for the period.
He is able to read and write, and knows both Greek and Latin.
He is unjustly known as Mieszko II Gnuśny (the "Lazy," "Stagnant" or "Slothful").
He received that epithet due to the unfortunate way his reign ended; but at the beginning he acted as a skillful and talented ruler.
