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 (BBG 12.7):
When αυτος is in the nominative case and agrees with a noun, then it is an intensive pronoun.
αὐτὸς ὁ ἀνήρ or ὁ ἀνὴρ αὐτός = the man himself
ἀνδρός αὐτοῦ = of the man himself
When αυτος is preceded by the article in any case:
ὁ αὐτός ἀνήρ = the same man
τοῦ αὐτοῦ ἀνδρός = of the same man