Board Thread:Lore Discussion/@comment-170.64.0.72-20150924144941/@comment-4511886-20150924153854

The Soul of the Last Giant's description confirmed this, although this was a fairly popular theory even before the SotFS update which updated said description to say the following:

''The lord of the Giants, who had brought wreck and ruin to the entire kingdom was said to have been felled by an unknown warrior. His beaten and broken remains were then dragged beneath the stronghold, where he was sealed away.''