So fas we do not have many information about him. He was called the "King of stockings/socks". He most probably had a factory for an own production.
His surname is Klajn in the Serbian version, in German Klein. This German-sounding name, meaning small, may indicate that he was Jewish. Old advertisements from his business were published in Serbian, German and Hungarian. Depending on the language, he transliterated his last name.
Sources
Buildings
Novi Sad (Нови Сад), Serbia
Palace Klajn