Geirrod (“spear-rider”) was a frost giant and the father of two giantess, Gialp (“yelper”) and Greip (“gripper”).
Geirrod and his two daughters tried to kill Thor. Though Geirrod managed to get Thor to leave behind his weapon, Thor received an unbreakable magic staff; a girdle of might and iron gauntlets from a giantess named Grid. Thor used the staff to defeat Geirrod’s daughters, and the iron glove (Jarngreipr) to kill Geirrod.
Note that Geirrod, the giant, should not be confused with the king in Grimnismal (“Grimnir’s Saying”) of the Poetic Edda.