Secluded Subterranean Stellar Species

The Omega Men and their mortal foes the Gordanians only occasionally ventured to Earth-One. These beings infrequently interacted with that world’s heroes including members of the Justice League (such as Green Lantern and Superman) and the New Teen Titans (including Robin and Kid Flash). In contrast, the Sub-Men and their rival race known as the Underlordians migrated permanently to Earth-Two’s subterranean realm, and battled members of the Justice Society (such as Green Lantern and Superman) and the All-Star Squadron (including Robin and Johnny Quick).

While the Omega Men were biologically diversified sister species with common traits residing on the Vegan worlds, the Sub-Men were genetically homogenized species with identical traits from their Vega’s parallel planets. As to the reason why the Sub-Men and Underlord’s empire left their native star system and took up residence underneath Earth-Two, this is yet to be told.

Gordanians had been shown exercising dominion in the Vega system when the Earth-Two Batman and Robin previously visited them, whereas that alien species’ doppelgängers in Earth-One’s universe were subservient to the Citadel. It appears a faction of Gordanians under Ayrn the Underlord's rule attempted to expand their empire to Earth-Two, perhaps enslaving the Sub-Men whom they brought with them. Their counterparts likewise invaded the New York City of Earth-One, beaten back by Robin and his New Teen Titans allies.

Another subterranean species that seemingly migrated to Earth-Two’s cavernous world below the surface were the Mole Men. Led by King Blakfu, a recurring enemy of Wonder Woman, as he was the counterpart of Kanjar Ro who repeatedly fought the Justice League of Earth-One, he and his minions were from the Antares star system. Kanjar Ro was exiled by his people while Blakfu retained rule over a small faction. His people sought greener pastures in the Sol system. 

While the Omega Men prospered upon their return to the Vega system, the Sub-Men became stagnate after initially regressing to a barbaric state, when the supervillain Ultra-Humanite found them. After exploiting them as hired henchmen for a time, sending them to distract members of the All-Star Squadron, once they served their purpose Ultra had most of them incinerated.

As for the Gordanians and their Citadel overlords, they met crushing defeats at the hands of both the Omega Men and their allies the New Teen Titans. Their cosmic twins led by Ayrn the Underlord likewise was humbled while battling the Justice Society of America, although he and his people were allowed to continue to exist within their underground metropolis. It seems quite likely that these creatures had previous encountered Blakfu’s Mole Men, as they both resided the arctic tundra. 

Another alien race attempting to colonized Earth-One was the Aquarians, who three times attempted to demolish the city of Fairfax in order to implement climate change, which would allow their species to exist on that world. Motivated by the pending loss of their own homeworld due to their sun turning super-nova. Each time, they were thwarted by the power personas of Chris King and Vicki Grant, who could Dial H For Hero. Their counterpart race in Earth-Two's universe were amphibious creatures drawn to that world by the Master Summoner, who were opposed by Doctor Fate along with his Justice Society allies.

A common factor as to the allure for these aliens to move to Earth-Two is its key location within its universe, as attested to by the oldest humanoids of that dimension, the Buddak. That said, Earth-One likewise during the 20th century became a refuge for extraterrestrials. Only in those instances, these came from different planets, such as the millions of miniaturized shrunken Kryptonians in the bottled city of Kandor, and political dissidents from Qward in the Anti-Matter universe now on Earth-One.