Lodomer or Ladomer was presumably born in the 1230s, not long before the First Mongol invasion of Hungary. He had an unnamed sister, the mother of Thomas, also an Archbishop of Esztergom, who studied in the University of Padua, courtesy of Lodomer. His ancestry, parentage and kinship relations have long been disputed among historians. Based on alleged "old manuscripts", 18th-century historian Miklós Schmitth claimed Lodomer originated from the territory of the Kievan Rus', and was a relative of Rostislav Mikhailovich and the Rurikids. (Lodomer can be interpreted as a Latinized form of the Slavic name Vladimir.) It is presumable that, in fact, Schmitth deduced that conclusion only from the prelate's forename and its similarity to Ruthenian principality Lodomeria. Referring to a papal letter allegedly from the end of the 13th century, historian János Török also argued in favour of the Ruthenian ancestry in 1853. He argued Lodomer's real name was John and called himself "Lodomericus" ("a man from Lodomeria") after arriving to Hungary. However contemporary scholar Nándor Knauz proved that papal letter was written 100 years later, at the end of the 14th century, and it referred to then archbishop John Kanizsai.