Mogo's origin and induction into the Green Lantern Corps has yet to be revealed. The planetform rarely is involved with others, its large size precluding any visits to Oa. However, a number of travellers have visited the Green Lantern.
Bolphugna the Unrelenting was a creature of violence who had bulit a reputation from numerous fights he had won. He intended to beat the most feared and mysterious being of them all... the Green Lantern known as Mogo.
The search for his quarry led him to an Earth type planet, devoid of any signs of intelligent life. Bolphugna called for the Green Lantern to face him. Receiving no response, he searched the planet for the Green Lantern.
Bolphugna's task was made all the more difficult by the fact that no one had any information as to what Mogo actually looked like. This would not stop him. Bolphugna spent years searching for the Green Lantern, examining plants, animals and insects. He grew more methodical in his search, surveying and drawing maps of the terrain. Although Bolphugna could find no intelligent life, he noted the forests seemed to be groomed in strange patterns, with large tracts of open land.
One night, entirely frustrated by his search, Bolphugna spread the maps out in front of him. Placing the ends of the maps together, the strange patterns of the trees made out the symbol of the Green Lantern Corps. Bolphugna quickly realized the very planet he was standing on was the Green Lantern known as Mogo. For the first time ever, Bolphugna the Unrelenting... relented. He ran to his starship, took off, and has not been heard of since.
As a planet and a Green Lantern, few things threatened Mogo. He did have difficulty with a meteor shower of corrosive yellow matter. The "scorch stuff" would burn into Mogo, his ring was powerless against the falling debris. To this end, Mogo created a holographic agent to barter with the star travelling Cluster, operated by Manga Khan. The hologram traded two canisters of the corrosive, held in an inert state, for two space dolphins caught by the Cluster.
Unknown to Manga Khan, the space dolphins were protected by Lobo. The bounty hunter tracked his dolphins to the Cluster, intending to kill those responsible. The superhero Mister Miracle was on hand to suggest he and Lobo track the dolphins to their new owner.
Their descent to the planet was disrupted by a sudden, extremely localized storm. There was no sign of habitation on the planet's surface. Lobo's call to the dolphins was ignored, an attempt to take them caused the planet to attack.
When the pair were immobilized, they were visited by a green hologram. He described himself as a servant of Master Mogo, and explained the situation to the trespassers. The dolphins ate the corrosive material, which they needed for their diet. They told Lobo they wished to stay on the planet. Lobo was invited to visit the dolphins provided he came in peace.
Realizing the dolphins would be safer with Mogo, Lobo and Mister Miracle returned to the Cluster. The pair never realized Mogo was a Green Lantern.
Another story of Mogo is a prophesy of the future. On Ysmault, the homeworld of the Empire of Tears, a prophecy was told to Abin Sur by a demon named Qull of the Five Inversions. According to the demon, the enemies of the Green Lantern Corps will rise united against them in final battle. Mogo will be the last to fall as Ranx the Sentient City explodes a blink-bomb within his core.
Recently, the Corps was destroyed by the actions of Hal Jordan. According to Green Lantern John Stewart, the planetform somehow "ceased to be", though accuracy of this statement is debatable. The last wielder of the power ring, Kyle Rayner, and J'Onn J'Onzz, the Martian Manhunter brought to Mogo an alien ark intent on preparing the Earth for seeding. The pilot had died years before and was absorbed into the macinery of the ship but was still programmed to fulfill the final mission. Rayner had the Martian Manhunter lead the ark to Mogo where it could change the planetform to match the environment of the long extinct race.
As the future is not yet written, it still remains possible for Mogo and the Green Lantern Corps to return. It remains to be seen what effect the new life on Mogo will lead to and if the Empire of Tears prophecies will come to pass.