In the late 1980s, Walt Simonson brought a new vitality to the character Thor, bringing in elements of Norse mythology that had seldom, if ever, been used in the title. In this 1987 issue, Simonson and artist Sal Buscema introduced the character Grendell who fights alongside of the Dark Warriors of Svartalfheim and who, if not for the interference of Loki, likely would have succeeded in killing Thor. In the story, Grendell relates that his mother had cast a spell that prevented him from being killed by iron, which is helpful in the plot, and that she had also been the reason that he had not died ages earlier.
Grendell later appeared in Incredible Hercules #136 in 2009.
(Note: this character has no relation to the character Grendel of Vanaheim from Marvel's Conan the Barbarian #127, co-written by J.M. Dematteis and Gil Kane and illustrated by Kane.)
More information on the character can be found here: http://www.marvunapp.com/Appendix4/grendellthor.htm
Grendell later appeared in Incredible Hercules #136 in 2009.
(Note: this character has no relation to the character Grendel of Vanaheim from Marvel's Conan the Barbarian #127, co-written by J.M. Dematteis and Gil Kane and illustrated by Kane.)
More information on the character can be found here: http://www.marvunapp.com/Appendix4/grendellthor.htm