The only giant you find that sounds, looks, and fights like the Last GIant is the Giant Lord in the giant memories. Think about it, there are many giants in the giant memories with slightly different looks and sizes but none look like the Last Giant except the Giant Lord. I believe that the GIant Lord becomes the Last Giant because the hero that defeated him bound him, it didn't say he killed him. And even another interesting and controversial idea arises: The Bearer of the Curse is the hero that brought down the Giant Lord and the momories of the giants are time portals! That idea is a stretch but the Last Giant totally was the Giant Lord!
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.