Thotan was a power scientist and warrior on his home planet of Nagbor. The warriors of Nagbor were at war with the Joxanda and needed a weapon that would turn the tide to their favor. The physiology of the Joxanda caused them to suffer a deadly reaction to oxygen, however Nagbor was severely deficient in this resource. The warriors located Earth, and found that the remote world contained an abundant supply of the deadly gas.
Thotan was sent to Earth to take all of the oxygen from the planet. He landed in the great North West of America and used his massive lungs to inhale the atmosphere for transport back to Nabgor. Thotan was tracked down by the Green Lantern who intercepted the alien invader and attacked. His power rays were no match for the giant, who shrugged off the blasts with ease. Standing 3,000 feet tall, Thotan proved a difficult challenge until Green Lantern used his power ring to enlarge himself.
Now eye to eye with his foe, Green Lantern reasoned that the giant had probably never had to use his fists before. The heroes superior fighting skills enabled him to land blow after blow on Thotan; however, in addition to his strength, the giant possessed incredible mental abilities. He was able to "read" the Green Lantern's fighting moves from his mind and quickly seized the advantage. Thotan tackled the Lantern and the two combatants came crashing down into a small mountain town. Green Lantern noticed that they hand landed near a general store just moments before Thotan could deliver a crushing blow. Quickly reaching out, the Lantern grabbed a keg of pepper and smashed it into his foe's face, momentarily distracting him. The Lantern then landed a knock out blow rendering Thotan unconscious. From there, it was easy to expel the stolen oxygen from Thotan's lungs.
The Green Lantern carried his prisoner back to his home planet Nabgor and delivered a message to the warriors of that planet. The Lantern warned them to stay away from Earth or suffer the same fate as their champion.