In chapter 10 of the Saga of the Völsungs, Sigmund's son Sinfjotli dies. His corpse is presumably carried to the underworld by a mysterious boatman, in a manner reminiscent of the Greek ferryman of Hades, Charon:
So Sinfjotli drank, and straightway fell down dead to the ground.
Sigmund rose up, and sorrowed nigh to death over him; then he took the corpse in his arms and fared away to the wood, and went till he came to a certain firth; and then he saw a man in a little boat; and that man asked if he would be wafted by him over the firth, and he said yes thereto; but so little was the boat, that they might not all go in it at once, so the corpse was first laid therein, while Sigmund went by the firth-side. But therewith the boat and the man therein vanished away from before Sigmund's eyes.
Source: The Story of the Volsungs, translated by William Morris and Eirikr Magnusson
Who is this mysterious psychopomp? Is he mentioned in any other Norse legend?