May contain plot details
Grimsen is a short, wizen faerie with a cloud of silver hair. He wears expensive and fancy clothes. When he bows before King Cardan, his posture is one of subservience but his gaze is greedy. There are seven heavy gold hoops in his large, pointed ears. His face is worn and leathery. His body is wiry and hairy.
He wants glory and wants a king who can give him that. He seeks greater and greater fame. Grimsen loves to be flattered. He wanted his creations to last forever so he frequently placed curses on them without telling the purchaser. This contributed to his exile with the former Alderking.
It was said that Grimsen could make anything out of metal, even living things like "metal birds that fly" and "metal snakes that slither and strike". He made the twin swords, Heartseeker and Heartsworn, one that never misses and the other that can cut through anything. Grimsen also made swords for the Alderking and was exiled when the Alderking was exiled.
Justin Duarte had sought Grimsen out to learn his secrets and show him a blade he had crafted.
Returning to the High Court
When Cardan Greenbriar was made the new High King, Grimsen came to the Palace of Elfhame to ask that his exile be lifted and that he might be allowed to return to the High Court. Grimsen promised that if his wishes were granted, he would be loyal to High King Cardan. However, when High King Cardan agrees, Grimsen says he will show his loyalty through his deeds rather than words.
Working with Madoc
Grimsen is later found at Madoc's camp in the Court of Teeth, where Jude Duarte flatters him and he invites her to his forge. He revealed to Jude that he curses everything he makes so that it will last forever.
Later, when High King Cardan breaks the blood crown, Grimsen panicked, knowing his curse would be awakened. He was then killed by High King Cardan, who had turned into a gigantic serpent.