Personal pronouns declension is regular except for ben/sen in dative and ben/biz in genitive. Siz can be used as singular in formal contexts with higher rank or strangers. Biz is rarely used for oneself, expressing humility or irony. Genitive onun cannot refer to sentence subject
Pronouns replace nouns in sentences. Pronouns come from "pro" (substitute) + "noun". Pronouns can be used as subjects or objects