He is described in the Wielkopolska Chronicle, written in the 14th century, where he is said to have taken power in Poland after the death of his father Mieszko II, as he was the eldest son.
The text describes him as follows: When he [Mieszko II] died in the year of our Lord 1033, he was succeeded by his first-born son Bolesław.
Bolesław meanwhile, because of his severity and the horrors of his crimes, badly ended his life, and though he was awarded the crown royal, shall not be placed among the Polish kings and princes.
This year Bezprym was killed by his own men, not without the instigation of his brothers, because of his cruelty and tyrannical rule.Bolesław's life is also described in a text written by Wincenty z Kielczy (13th century) and some other sources.
They had the following arguments: Some say that Gallus Anonymus failed to describe Bolesław because of the ruler's part in the pagan reaction in Poland.