Threats To The Viking Gods

Poul Anderson, The Broken Sword (London, 1977), Chapter XXII, p. 158.

Threats To The Gods
Asa-Loki
Utgard-Loki
Hel
Fenris
Jormungandr
Garm

Asa-Loki seems to mean just "Loki." OK. "Asa" seems to mean just "As," of which the plural is "Aesir." See here and here.

Utgard-Loki is a Jotun.

Hel is the ruler of the realm of the same name and a daughter of Asa-Loki. I thought that she was called "Hela."

Fenris is the wolf that will devour Odin and a son of Asa-Loki.

Jormungandr is the serpent that encircles Midgard and a son of Asa-Loki and will kill and be killed by Thor.

Garm is Hel's watchdog, will devour the moon and will kill and be killed by Tyr.

Thus, here we have two Lokis, three off-spring of one Loki and one other being. Fenris, Jormungandr and Garm will kill Odin, Thor and Tyr, respectively. For good fictional versions of these characters, read:

Poul Anderson's heroic fantasies;
Mark Millar and Bryan Hitch's The Ultimates (and see here);
Neil Gaiman's The Sandman;
Mike Carey's Lucifer -

- and see Marvel films.