Personal Pronouns: Genitive (whose?- case)
Used for expressing possession:
my, mine; your, yours, his .....
after certain prepositions:
away from ἀπό,
behind ὄπισθεν,
with μετά, etc.
  1st person singular:    my father.
   behind me (stressed, emphasised)
   behind me (neutral, unstressed "me"
  ὁ πατήρ μου
  ὄπισθεν μοῦ      
  ὄπισθέν μου
  2nd person singular:      your father.
   behind you (stressed, emphasised)
   behind you (neutral, unstressed "you"
  ὁ πατήρ σου
  ὄπισθεν σο
  ὄπισθέν σου
  3rd person singular:
 
Greek masculine:        his father.
   behind him
  ὁ πατήρ αὐτοῦ
  ὄπισθεν αὐτοῦ
Greek feminine:        her father.
   behind her
  ὁ πατήρ αὐτῆς
  ὄπισθεν αὐτῆς
Greek neuter:        it father.
   behind it
  ὁ πατήρ αὐτοῦ
  ὄπισθεν αὐτοῦ
 
  1st person plural:    our father.
   behind us
  ὁ πατήρ μῶν
  ὄπισθεν ἡμῶν
  2nd person plural:      your (pl) father.
   behind you (pl.)
  ὁ πατήρ μῶν
  ὄπισθεν ὑμῶν
  3rd person plural:      their father.
   behind them
  ὁ πατήρ αὐτῶν
  ὄπισθεν αὐτῶν