Ladislaus (also Lack) was born into the prestigious and influential "gens" (clan) Rátót, as the son of Stephen I ("the Porc"), who was a strong confidant of Queen Elizabeth the Cuman and held several offices in her court since 1265. It is plausible that Stephen's only known wife Aglent Smaragd was not the mother of Ladislaus; she was still alive in 1327, and was a Beguine nun at the Sibylla cloister in Buda. Her brothers, Ladislaus and Aynard were active courtiers even in 1350. Ladislaus had four known brothers: the eldest one, Dominic II was considered actual head of the family and a powerful baron for decades. Lawrence was killed in the Battle of Lake Hód (near present-day Hódmezővásárhely) in 1282. Kakas perished in the Battle of Rozgony in 1312. The youngest brother was Leustach III (also "the Great"). He was first mentioned by contemporary records only in 1338, thus he was presumably much younger than his late brothers, and his mother was perhaps Aglent Smaragd.