Heidrek is the human viking son of King Hofund of Glaesisvoll and the viking woman Hervor, and a bearer of the cursed sword Tyrfing. By his mother's line he is a great great great great grandson of Odin.
Angantyr was the brother of Heidrek, and both grew to be tall and handsome men. Angantyr, the gentle, was best beloved of his father King Hofund, while his brother, the violent Heidrek, was favorite of his viking mother Hervor.
Heidrek inherited the cursed sword Tyrfing from his mother. During a banquet, Heidrek started a feud which caused the death of two men, and the king declared him an outlaw. To punish his father, he drew the sword Tyrfing and slew his own brother, the king's beloved son Angantyr.
After this, Heidrek was forced to leave his homeland became a viking captain.
AD&D 1st edition
Game statistics for Heidrek appear in Giants in the Earth, Dragon #42 (Oct 1980), p.35, where he is a 15th level fighter.
Heidrek appears in the in the 13th century Icelandic saga Hervarar saga ok Heiðreks (The Saga of Hervör and Heidrek).
In the original, Heidrek attends a feast to which he has not been invited. Angantyr, his brother, offers him a seat. Heidrek intentionally goads two adjacent men into fighting one another, resulting in one's death. Hofund throws him out, so he throws a stone back at the building, accidentally killing his own brother. For this he is sentenced to outlawry, but his mother gives him the sword Tyrfing to take with him.
Heidrek thereafter has a daughter, who he names Hervor, and son, who he names Angantyr.