Originally posted by: Pervert-Sennin Jiraiya
why would akatsuki want to summon the strongest creature in the world which is impossible to kill?
If it lives it can be killed. And I'd like to point out that the two first Hokages were deceased. The Ninetails is not dead-yet. Also, I believe that a summoning contract is required to summon a living being (i.e the contract Naruto signs to summon frogs) and therefore someone would have to get a contract with desired creature/demon/person to be able to summon them. A dead person can not agree upon a contract, and therefore a contract would not be needed.

Looking at this from a different angle, living beings have some sort of conscience that distinguishes us from other people. I am similar to many other people in terms of personality, looks, condition, etc, but there is no one that is exactly like me. Of course, a dead person does not have this, and it can be argued that that is the *person* and the body is a vessel. Therefore, if someone summoned up dead people they would have to substitue for those souls so that the summoned person is more than an empty shell standing there.

Just some theory for the academics.