Gullveig is a name meaning “gleaming one” or “gold branch.” Gullveig was a Vanir who had a lust for gold. She went to Asgard and could speak of nothing other than gold. Her lust was such that the Aesir could not deal with it anymore and so they burnt her.
Gullveig could not be killed, but emerged from the fire unscathed. Perplexed by this, they tried to burn her a second time. Again she came forth unharmed from the flames. They burn her a third, but as she emerged they knew not what to do with her. The Vanir heard of how Gullveig had been treated and were incensed. They retaliated, beginning the first war.
I read a rather interesting theory about Gullveig and Freyja being one and the same. I cannot recall exactly where I read this, but the author stated that because there is no story about the first time Freyja ever visited Asgard, or any story as to how she came to be accepted there even though she was known to be quite close to Odin.
Gullveig and Freyja also shared other aspects; they were both seers and Freyja is known as the mother of Seidh magick. It can also be theorized that they shared the lust for gold if we look to the story of Brisingamen.
Brisingamen was a necklace that the blacksmith dwarves (Dvalin, Berling, Alfrik, and Grer) made, purported to be of gold. Freyja was so taken by it that she simply *had* to have it and so agreed to sleep with the dwarves in trade for it.
Personally, I do not believe that Freyja and Gullveig are the same person. The person who devised this theory only connected the dots rather superficially. For instance, brisingamen was certainly a pretty necklace, but it also gave the wearer irresistable charms and luck to win in battles.
I could go on and on, but the fact is there is no way to know if my theory or theirs is more correct. It is through a personal relationship with the pantheon that one can decide best. What are some of your theories/ideas?