One of Fenrir's most recent fictional namesakes is the werewolf and wannabe death-eater Fenrir Greyback, who first appears in Harry Potter and the Half-Blood Prince.

Wonder where Rowling got the idea? Before Fenrir Greyback, there was Fenris Ulf (in some editions called Maugrim), the brutal wolf-in-chief of the White Witch's secret police in C.S. Lewis's The Lion, the Witch and the Wardrobe.

Fenrir's name means "fen (swamp)-dweller" in Old Icelandic. Could it be that his island prison isn't exactly a paradise? (Source p. 42)

The creators of the Mu Online computer game must have thought Fenrir missed his calling as a horse, because they named a race of giant wolf-mounts after him.

Like many of his fellow mythological beings, Fenrir gets to have an astrological body named after him; in this case, a recently-discovered moon of Saturn. (Source.)