Exiles of the Planet Oa Terrorize the Multiverse

Early in the history of Earth-One's universe, a scientist of the planet Maltus named Krona had been obsessed with learning the secrets of the past. While on the world known as Oa, Krona used technology to witness the dawn of creation, something that had been strictly prohibited by his society as they had somehow become aware of the dire consequences for his actions. In fact, instead of attaining increased knowledge, Krona's contemptuous curiosity caused his own universe to be replicated an infinite number of times, spawning the Multiverse and the Anti-Matter Universe. For his crimes, his fellow Oans banished him to wander his universe by transforming him into a globe of energy. Not long thereafter, these same benevolent blue-skinned beings became the Guardians of the Universe.

Realizing that their own inherent evil might motivate them to do despicable deeds like that of the former brother, the Guardians purged all of their own negative energy and banished it in a globe of energy to wander Earth-Two's universe, where they had previously sent the Starheart. Once there, this malevolent globe gained sentience, much as its Earth-One doppelgänger, its Antithesis. Indeed the Guardians realized that the Starheart's energy would eventually locate a champion in that realm with powers similar to their own Green Lantern Corps, and were confident that this individual could combat the now sentient Evil-Globe.

And, in fact, this was accomplished when Alan Scott, wielding the green lantern and power ring, joined alongside his allies of the All-Star Squadron to vanquish this entity from Earth-Two when it merged with Joe Morgan in a fit of vengeance. The Evil Globe-Being merged with Morgan turned the former boxing trainer a gigantic being with a glowing bluish hue. Morgan aka "Nat Milligan" was the counterpart of Earth-One's Guy Gardner, aka the backup Green Lantern of Sector 2814. 

As for the Guardians’ self-replicating Evil-Globe, its cosmic twin was the Guardians’ Green Globs, sentient energy entities that assisted individuals throughout the universe. The benevolent Glob secretly intervened in the lives of numerous individuals throughout the 1960s, before leaving Earth-One just as the malevolent Globe had when it was exiled from Earth-Two during the early 1940s.

Decades later, another globe of energy arrived also on Earth-Two, only this was actually Krona who had merged with Alan's power ring. Leading Scott back over to Earth-One to meet up with his counterpart Hal Jordan, both Green Lanterns were soon summoned by the Guardians who advised them that Krona had reintegrated his physical body and threatened this universe. Side-by-side, this pair defeated the villain and consigned him once more into the void of space. 

A few years later, another immortal adversary of Green Lantern tied to a celestial object, the meteor-invigorated Vandal Savage, traveled from Earth-Two to Earth-One. Savage's goal was similar to that of Krona, to regain his physical vitality while dominating all others unopposed. However, he faced that world's Superman and Vandal's centuries old adversary, the Immortal Man, along with the Forgotten Heroes, who thwarted his sinister schemes. He apparently returned to Earth-Two following his defeat.

The counterpart of Krona, Ghan Uu, was one of three Buddak's from the planetary twin of Maltus who invaded Earth-Two a few years after Krona's incursion on both worlds, only he and his allies were defeated by Doctor Fate and a visiting Superman of Earth-One, who mirrored the Green Lantern's in their heroic actions in facing their age-old adversaries. While Krona returned from seemingly being wiped from existence, Ghan Uu and his two confederates perished at the conclusion of the cosmic crisis they attempted to unleash on Earth-Two and their universe.