Jews specifically invited to Poland (to join the existing Jewish populace) by Casimir the Great.
Casimir III of Poland (1310–1370 CE) was the last king of Poland from the Piast Dynasty (1333–1370 CE).
On October 9, 1334 he had confirmed the privileges granted to Jewish Poles back in 1264 by Boleslaw V the Chaste. Under penalty of death, Casimir prohibited the kidnapping of Jewish children for the purpose of enforced Christian baptism. He inflicted severe punishment for the desecration of Jewish cemeteries.
Casimir was the son of King Wladyslaw I the Elbow–high and his wife Hedwig of Kalisz (for those who track these matters). As he had no sons, Casimir was succeeded by his nephew, King Louis I of Hungary.