During the formation of the hidden villages, the First Hokage sought the Uzumaki's help to seal the Nine-Tails and other tailed beasts. This established the Uzumaki as the foremost seal masters ...

The Reaper Death Seal summons a shinigami to bind the summoner's and the target's souls to the shinigami. Minato used this seal to lock the Yin side of the Nine-tails in himself right before he died.