Thaal Sinestro was once the greatest member of the Green Lantern Corps, being lauded by the Guardians of the Universe for his many deeds. He mentored and inspired many Green Lanterns, including Hal Jordan, who would later uncover Sinestro's more unsavory traits. Obsessed with order, unhinged by conflict on his homeworld of Korugar, and corrupted by his own power, Sinestro became a tyrant and one of the greatest threats the galaxy had ever seen.