What is the last name of akatsuki?

Akatsuki isn't a person therefore it doesn't have a , it is an organization of rogue ninja, consists usually of 10, that have defected from their village. You know the ninja's that wore the dark robes with red clouds on them with chin high collars? Itachi

"was" one if that rings a bell but he was in it for different reasons which are revealed later in the shippuden series.