He was the fourth son of Mieszko I of Poland, the third born from his second marriage with Oda, daughter of Dietrich of Haldensleben, Margrave of the North March.
Lambert's first appearance was in the document called "Dagome iudex" (ca.
After Mieszko I's death (25 May 992), the war began between Bolesław I and his half-brothers for the paternal heritage, a dispute which according to some historians lasted only a few weeks, and according to others, only finished in 995.
Despite the tensions between both parties, Bolesław I's first son with Emnilda of Lusatia was probably named after him; it's expected that the choice of this name for his son was an expression of warming relations between Bolesław I and his stepmother Oda.
[1] At the end, Bolesław I took control of the country and expelled his stepmother and half-brothers from Poland to Germany.