αυτος is usually the third person, personal pronoun.
masculine | feminine | neuter | ||
singular | nominative | αὐτός | αὐτή | αὐτό |
genitive | αὐτοῦ | αὐτῆς | αὐτοῦ | |
dative | αὐτῷ | αὐτῇ | αὐτῷ | |
accusative | αὐτόν | αὐτήν | αὐτό | |
plural | nominative | αὐτοί | αὐταί | αὐτά |
genitive | αὐτῶν | αὐτῶν | αὐτῶν | |
dative | αὐτοῖς | αὐταῖς | αὐτοῖς | |
accusative | αὐτούς | αὐτάς | αὐτά |
It has two other functions as well; see principle 19 and principle 48.