Dheron is the fifth planet of the Rao star system orbiting the same sun as the planet Krypton, which is the fourth.
Its natives evolved at the same rate as the Kryptonians, but their path was harder. Dheron's climate was more difficult and their resources fewer. Dheronians developed limited-range space flight at roughly the same time as their neighbors, but their distance was too great to allow travel between the two worlds.
However, once every twenty years their orbits were close enough for contact, igniting a war between the two worlds. Both worlds were sabotaging each others' advancements in space travel to make sure none had the advantage, until one day Dheron was visited by the rogue Kryptonian Zod-El. Zod gave them the means of finally destroying Krypton and the technology of interstellar travel, and in return they will seek and destroy any surviving Kryptonian that manages to escape.
Tyrell was among the soldiers sent to follow the last Kryptonian among the stars to finally end the long war, and should he fail he will send a distress signal to lead Zod-El to the last Kryptonian in order to eliminate him himself.