A prepositional pronoun is a special form of a personal pronoun that is used as the object of a preposition.
English does not have a distinct grammatical case that relates solely to prepositional pronouns. Certain genitive pronouns [1] (e.g. a friend of hers; that dog of yours is as friendly as mine) both complement prepositions and also may function as subjects. Additionally, object pronouns (e.g. watch him; look at him) may complement either prepositions or transitive verbs. In some other languages, a special set of pronouns is required in prepositional contexts (although the individual pronouns in this set may also be found in other contexts).