Not sure where the whole "Frost" part came from, but I believe the Jötunn were just giants in Norse mythology. And their appearance could differ dramatically between individuals, with some being described as "exceedingly beautiful", and others as "alarmingly hideous".
On a side note, Loki is also a god of chaos and magic.
Odin is also a god of magic in Norse mythology, and Freya is also a goddess of magic. Now that I think about, Norse mythology has a lot of magic-gods . . .