Went on victory streaks between each of his Official Personal stalker I will follow you shirt two losses in a time when streaks in MMA were few and far between. His losses came from two very high level competitors. Matt Hughes was a beast of a champion when he beat and doubled down, trained harder than ever, came back and beat him easily the next time they matched up. He basically took himself to a whole other level and dominated top tier challengers like BJ Penn, Hughes, Sherk, Serra, Hendricks, etc. Penn and Hughes were distinguished champions and legends in their own right and he defeated them both twice.
He, also, was a Official Personal stalker I will follow you shirt champion in two divisions, and if I remember correctly, he may have been the first to do that. He was one of the first in MMA to have a long title defense streak as well, with Penn and Hughes being the nearest competition for that title until Silva came along. Prior to that era, it was unlikely for a champion to defend the title more than a couple of times before being dethroned. In his prime, GSP looked nearly unstoppable. Top tier guys struggled to even score on him in a fight, typically being taken down and pounded round after round. It was reminiscent of the Khabib Nurmagomedov reign we see today. Total ring control and dominance. Top pro fighters looking like amateurs when in the ring with him.