The Clan Chieftain of local Fire Giants hailing from the Crystalmist Mountains who led the attack on Pest’s Crossing during the Giantish Invasion of Geoff in 583 CY.

Shortly after the assault, Mogthrasir claimed responsibility for the entire invasion and proclaimed himself the “King of Geoff”—naming Pest’s Crossing as the new capital of Geoff. It is unknown what his motivation was for uniting the giant clans of the Barrier Peaks and Crystalmist Mountains or why they chose to come down in force out of the mountains after almost one thousand years of relative peace.

Between 583-585 CY Mogthrasir is reported to have strengthened the defenses of his new capital by erecting a stone fortress called Castle Thrasmotnir upon an artificial hill on the northern outskirts of town as well as overseeing the construction of a great moat that now rings the fortress and city itself.