The only one who is called AMIR ALMOMENIN.
One day the prophet was with some of his followers at the mosque,saying that whoever enters this room now,will be the leader and the Imam after me.Everyone was waiting to see who was going to enter the mosque.After some time, they heard a man walking through the door.It wasn't long befor Ali arrived with his usual meek expression.
The prophet
got up and hugged him saying,"God has informed me that Ali will indeed
be your leader and guardian after me.The other thing is that I command
you to call Ali by this title from now on:AMIR-ALMOMEMIN(Imam of
belivers).Nobody has ever deserved this title before nor will be
entitled to it in the future.AMIR-ALMOMENIN can only be used as Ali's
title."