Name: Kuchiyose: Edo Tensei, 口寄せ・穢土転生, literally "Summoning: Impure World Resurrection", English "Summoning Jutsu: Reanimation"
Type: Kinjutsu, S-rank, Supplementary
This forbidden summoning technique allows the user to revive the dead. The user must first sacrifice a living human in order to tie the deceased person's soul to the world (unlike the normal summoning technique, which only requires some of the user's blood). The sacrificed body is then surrounded with dirt and dust that compacts into the shape of the summoned soul's original body. The resurrected person then rises from the ground in a wooden coffin. At first, the person appears pale and dirty, as most undead are portrayed. The user has to restore their appearance through a special seal.
When revived, the person retains all of their memories. Because of this, the revived person is not completely under the user's control. With the same seal that restores the revived person's appearance, their free will can be erased, thus putting them under the user's complete control. The summoned person can't be killed and any damage to them regenerates. The soul must be removed from the body in order to kill the resurrected person. This technique can also be used to summon multiple people at once, depending on the amount of sacrifices and the chakra level of the user.
Orochimaru uses this technique during his battle with the Third Hokage in the Invasion of Konoha arc to summon the First and Second Hokages. He had also intended to summon someone else, but the Third prevented the final summon. In the anime, the coffin partially rises from the ground, and the symbol 四 on it suggests that the Fourth Hokage was the final summon. In the manga, the coffin did not appear as the Third stops the final summon before it can even be attempted, so the occupant of the coffin is left more ambiguous.