The two heroes are invulnerable, Achilles because he was dipped in the river Styx by his mother Thetis, and Siegfried because he took a bath in the dragon's blood.
Both have a weak spot though, Achilles in the heel, where his mother held him, and Siegfried in the back, because a leaf from a tree had fallen on him.
Is there any link between them? Was Siegfried myth influenced by the Achilles story? Do both myths have a common Indoeuropean origin?
I'm curious if there is any other similar story in other mythologies as well.