Cybertron

Cybertron is the home planet of the Transformers and (usually) the body of their creator, Primus.

Cybertron was well into the Autobot-Decepticon war when Megatron sought to spread his Dark Energon throughout the planet. After infecting the Cybertron's very core, Cybertron's surface was slowly starting to become covered in the dark substance. Optimus Prime and his team soon cleared the Dark Energon from the core, but it had been too badly corrupted. However, it could revitalize itself and Cybertron by shutting down for millions of years, so Optimus ordered an exodus from the planet, during which many Autobots fled to find a new home elsewhere, as Cybertron remained in darkness.

By the time Team Prime arrived on Earth, Ratchet noted that Cybertron had been dark for eons.

Megatron planned to use Dark Energon to reawaken Cybertron's dead as his own minions and sent a large chunk of Dark Energon through a space bridge from Earth to Cybertron. Upon impact, the Dark Energon awoke thousands of the deceased Cybertronians, which were commanded by Megatron to come through the Space bridge, leaving Cybertron more dead than before.