Loki (also knwon as: The Trickster, The Captain, Lucky, Sky Trekker, Wildfire, Crookmouth, Hawk-eye, Dogstar, The Betrayer, The doer of good and the doer of evil) is disliked and mistrusted by nearly everyone. He tricks and lies guiltlessly, he steals, and he cares about his life more than anything else in the Worlds, which led him to switch sides in the Winter War and fight against the Aesir and Vanir.
Unfortunately for him, everybody lost in the War and he was tossed into Netherworld. He was imprisoned in the Black Fortress with his son, Jormungand, as his guard and fellow inmate; and only means of escape.
After a few years in the Black Fortress and before the events of Runemarks, Loki struck a deal with his son asking for freedom, and promising freedom in return. Loki slipped down the snake's tail into the river dream and ended up in the Ridings, in Midgard. There he found his way into the body that he inhabits for the whole book.
He and Maddy meet as Maddy is looking for the Whisperer. He introduces himself as Lucky, but Maddy manages to see through his disguise and finds the violet rune kaen on his left forearm.