It was painstakingly constructed using Jorgey's Promethean slaves (before the Didact took control of them) and then it was subjected to massive Composer-ing by Jorgey on board the Long Night of Solace to make it a real planet. He then descended to the planet on the ship with his Storm Covenant fleet, and populated it with his Reachites, created from his genetic code.
The planet prospered afterwards, apart from a minor blip involving a war with the Galactic Council. The planet itself retained its stature as a well-respected world and it now has a joint Human-Reachite population, but the only Humans allowed to live there for a permanent time are those who are deemed to have felt the PAIN and are therefore elligible for sanctuary on New Reach.
Some Grunts are even allowed to live on New Reach, but they have to pass a Reachy test to get in. Its a paradise for Grunts on New Reach as they cannot breed there, so Jorgey does not need to eliminate the surplus population. The only drawback on this is that if Grunts do want to breed then they must do it off-world,