Thaal Sinestro is a fictional character, an alien supervillain in the DC Comics Universe. Created by John Broome and Gil Kane, Sinestro is the former mentor of Hal Jordan and the arch-nemesis of the entire Green Lantern Corps. Sinestro first appears in Green Lantern (vol. 2) #7 (July-August 1961). He is also revealed to be the father of Soranik Natu, a Green Lantern who currently holds his old post within the Corps. In 2009, Sinestro was ranked as IGN's 15th Greatest Comic Book Villain of All Time.
Sinestro was born on the planet Korugar in space sector 1417. His dedication to preserving order originally manifested in his previous career, an anthropologist specializing in reconstructions of ruins of long-dead civilizations. One day while he was on one such site, a Green Lantern named Prohl Gosgotha crashlanded into the site, injured and apparently dying. He quickly gave his ring to Sinestro, just in time for Sinestro, who barely even understood what the ring could do, to defend himself from the Lantern's pursuer - A Weaponer of Qward. However, Sinestro had to destroy the very ruins he had spent loving care restoring, to crush the Qwardian. Afterward, Gosgotha turned out to still be alive, and asked for his ring back to keep him alive long enough to get help. Sinestro, knowing this would mean not being a Green Lantern himself, instead allowed him to die and took over his post, the Guardians unaware of his actions.
In Green Lantern #45 we see for the first time his wife in a flashback and that it is, in fact, the sister of Abin Sur.
His desire for order did well by him in the Corps, and initially led him to be considered one of the greatest Green Lanterns. As the years passed, he became more and more fixated upon not simply protecting his sector, but on preserving order in the society of his home planet no matter the cost. Eventually he concluded that the best way to accomplish this was to conquer Korugar, and to rule the planet as a dictator.
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Official Site: DC Comics
Links: Sinestro Wiki Entry the Book of Oa MyKey3000