Xorda

The Xorda are a warlike alien species responsible for the metamorphosis of Earth into Mobius. They resemble large, purple, brain-like organs with long pink tentacles and a single green eye; they also communicate through telepathy. During the Great Harmony when of all the Chaos Emeralds in the universe were pulled towards Mobius, it was revealed that the Xorda's home world is the location of the blue Chaos Emeralds.

Attack on Earth

 * See: Xorda Attack on Earth

The Xorda's wrath was incurred upon Earth when an envoy they sent to it was captured, imprisoned, and dissected by human scientists. Outraged, the Xorda bombarded the planet with Gene Bombs, believing that all life had been wiped out. Unbeknownst to them, some survived, and eventually swelled to repopulate the planet. The energy of the bomb caused the mutation of many animal species into the anthropomorphic Mobians that now inhabit it, as well as the creation of Mobius' Chaos Emeralds. This latter fact was cast into doubt however when the source of this information - a 12,000 year old robot named Isaac - was revealed to have most of its data corrupted and/or erroneous when he was hacked into by Dr. Finitevus. (StH: #124, #125, #148)

Return

 * See: Xorda Attack on Mobius

The secrecy of continued life on Mobius was compromised when the Xorda discovered two ships heading for Mobius. Presumably they knew that there were Overlanders (humans) aboard as Hope Kintobor explained that they attacked them. Presumably they traced the ships to Mobius and realised that life had arisen again. Upon entering the Solar System, they nearly stumbled upon a ship from the Bem, a much more belevolent alien race, but were distracted by Shadow the Hedgehog. When they arrived, they delivered an ultimatum of destruction unto the people of Mobius, and also told them the truth about their world's origins. As if to demonstrate their power, they launched a devastating single-ship attack on Dr. Eggman's Eggman Empire. The ship was repulsed by Giga-Bot Prime, a giant robot created by Eggman that only Sonic's speed could power (presumably at that point in time, Eggman would surely have access to alternative power sources under normal circumstances). However, the Xorda had yet to play their trump card. (StH: #124, #125)

In the planet's polar region, the Xorda revealed their final plan to eradicate the planet. A pyramidal device, known as the Quantum Dial, was set up. Its purpose was to tear open a hole in reality, creating a black hole powerful enough to consume the planet and the entire solar system. It was assumed that such a large target would be easy to deal with, given that Station Square launched an immediate missile strike. However, the Quantum Dial possessed some kind of field that caused any construct within fifty feet to fall apart. Unwilling to give up without a fight, the various fighters of Mobius banded together, putting aside their differences to battle a common enemy. However, even with the amazing number of warriors aligned against them, the Xorda weapon was only vanquished after the timely resurrection of Knuckles the Echidna (who simultaneously caused the destruction of the weapon's defenses) and the seeming suicide attack of Sonic the Hedgehog upon the Quantum Dial, which caused the destruction of the device. (StH: #125)

The Xorda departed Mobius soon after they launched the Quantum dial leaving the entire planet for dead. They are also the reason that the Bem do not pursue a vessel (which heads on a course back to Mobius via a bem jumpgate) they believe to contain Ceneca 9009, the rogue scientist who built the De-Roboticizer. In truth, the vessel held Sonic, who had been beamed into space by the Quantum Dial's destruction. Unwittingly, the Xorda had inadvertently provided a safe journey home for their greatest hindrance. As the Bem pointed out that access to Mobius via their jumpgates was officially restricted on account of the Xorda having declared war on the planet - this would suggest the possibility that the Xorda are aware of their second failure to destroy all humanoid life on Mobius. (StH: #129, #170)

War with the Black Arms
Some time after Sonic's return to Mobius, the Xorda were engaged in intergalactic warfare with the Black Arms, another warmongering species, which prevented the latter's return to Mobius. (StH: #170, #171)