Torn from their homeworlds, dozens of alien cities were taken across space to Oa. They were each placed next to other alien cities, the playthings of the insane Guardian Appa Ali Apsa. One of the cities was from Xudar, homeworld of the late Green Lantern Tomar-Re of Space Sector 2813.
Tomar-Tu was among a trio of Xudarians who travelled to a neighboring Earth city, Hope Springs, formerly of West Virginia. The Xudarians had sought out allies but were attacked by the fearful humans. The fight was broken up by Green Lantern Hal Jordan who then went off to fight the mad Guardian. Jordan didn't have a chance.
Tomar-Tu was later contacted by Jordan and asked to use the Xudarian observatories to watch the skies for Guy Gardner, whom Jordan had summoned from Earth. When they signalled Gardner's arrival, Jordan took the forms of some of the alien races' messiahs to create a diversion, while he tapped into the ruins of the Central Battery.
For assisting the Green Lanterns, the Xudarians were punished by Appa Ali Apsa. Tomar-Tu's people were attacked by the Shugs and the Great Bats of the Iron Forest.
The Guardians of the Universe returned from their other-dimensional retreat to stop their mad brother. Once again, the Xudarians mounted a defense for the Green Lanterns. Tomar-Tu put himself in harm's way to rescue Hal Jordan. Through the combined efforts of the Guardians, Guy Gardner, Hal Jordan and Green Lantern John Stewart, Appa Ali Apsa's link to the Oan power was severed, killing the mad Guardian.
Tomar-Tu took part in an interspecies union, designed to improve relations between the alien races of the Mosaic world. Rose Hardin was one of the human representatives from Hope Springs.
In Greenville, another human enclave on Oa, two teenagers were killed by the neighboring alien race known as the Horde. This set off an anti-alien fervor among some of the humans on Oa. To stop the fighting, John Stewart raised a wall of rock between the humans and the Horde.
Instead of solving the problem, this only added to the paranoia of some of the humans. Tomar-Tu and other Xudarians visited Rose Hardin and were fired upon by Moses Rockwell's group. After the Xudarians learned of the attack on the delegation they responded with force.
This only added fuel to the fire, as the human group fired upon the Xudarians and invaded their city. John Stewart's reaction was to build walls aroung all the cities of the Mosaic.
The humans still believed Stewart was responsible for their situation. They would force him to move against them. They took Rose Hardin's translator to facilitate communication with other aliens who might wish to overthrow the Green Lantern.
Fighting broke out across the Mosaic. The great walls were torn down, humans and aliens were slaughtering each other. The arrival of Hal Jordan, Brik, and Chaselon was used by Stewart to separate the fighters. Stewart imprisoned the ring leaders in an Oan Sciencell, they would work out their differences or die in the process. Stewart then brought Tomar-Tu, Rose Hardin, and representatives from other species together to help build the Mosaic world.
The small group were discussing the establishment of a road to create an interdependence of the Mosaic cities when the meeting was disrupted. John Stewart had been contacted by Green Lantern Brik of Dryad to help battle Star Sapphire. Stewart wanted revenge for the death of his wife, Green Lantern Katma Tui-Stewart. Rose and Tomar tried to stop John from leaving, but were unsuccessful.
The fight with Star Sapphire was complicated by the machinations of the mercenary known as Flicker and a Teban war fleet led by Kreon of Tebis. Other Green Lanterns arrived to assist Jordan. The Green Lantern of Earth recruited Boodikka of Bellatrix to join the fight.
Star Sapphire was eventually subdued, and reverted back to her Carol Ferris aspect. To fulfill a deal with the Guardians, Jordan invited Tomar-Tu and Kreon to become Green Lanterns.
The new recruits trained under the supervision of Kilowog. He would tell them stories of the Green Lantern Corps and they would learn through the Great Book of Oa.
Following the warnings of Amanita, the Green Lantern Corps travelled to Earth to help fight Eclipso. The God of Vengeance had possessed Hal Jordan and the Corps was unable to free him. Star Sapphire had also been brought back, but Eclipso would be defeated by others.
Tomar-Tu was on hand during the Qwardian invasion of Oa. Inadvertantly led by former Green Lantern Guy Gardner, the Weaponers of Qward threatened to overrun Oa. The fledgling Corps was without Jordan or Kilowog, as the two Green Lanterns were still on Earth fighting Eclipso. Bitter rivalries between Boodikka and Kreon jeopardized the safety of Oa. Tomar-Tu had to convince Kreon to call for help. The Weaponers were forced back by Gardner after he had achieved his only objective, the retrieval of the yellow ring of Sinestro.
The rift between Boodikka and Kreon would later be healed by the intervention of John Stewart. Kilowog brought the recruits to Stewart to learn how to work together. Stewart made the two rivals face their fears and learn to work together.
The return of renegade Guardian Krona as the incarnation of Entropy was another turning point in the history of the Corps. The Guardians ordered the Green Lanterns to battle Entropy so their own immortal lives would not be shortened. Though Tomar-Tu did not fully believe in the cause, he would protect his fellow Green Lanterns.
Tomar-Tu was called to Maltus to aid Hal Jordan and the rest of the Green Lantern Corps against the Triarch. On the Guardians' homeworld, the Green Lanterns fought alternately against and alongside the L.E.G.I.O.N. and the Darkstars.
Tomar-Tu's final mission was against his friend Hal Jordan. He had to prevent the Green Lantern of Earth from reaching Oa and absorbing the Central Power Battery. Unfortunately, Tomar-Tu was no match for the superior ability of Jordan. The Xudarian's power ring was taken to augment Jordan's growing power. Whether Tomar-Tu lived or died has yet to be revealed.