The Xorda are a warlike alien species found in the sonic universe (Archie Comic). They are somehow capable of intergalactic travel despite residing in an aquadic enviorment. In the 21st century of Earth, their emissary came to offer an aliance with the humans, but was captured and dissected by Dr. Ivan Kintobor and his science team. Enraged, the Xorda attacked earth using Gene Bomb weaponry. They then left Earth, thinking they had killed all human life, when in reality the surviving creatures attained human DNA and evolved into what are now known as Mobians, and Earth was renamed Mobius by the new inhabidants.
History
After their envoy was captured, imprisoned, and then dissected, they attacked earth with Gene Bombs; and, believing that all life was irraticated, they left earth. They were, however, unaware that the survivng animals mutated with human DNA and became what we now call Mobians, and the remaining humans were slightly mutated, and de-evolved into what are now known as Overlanders: the energy from the Gene Bomb also created the Chaos Emeralds.
Not much is known about the Xorda, such as what their culture was like, what their religion was (assuming they even had one), etc. This leaves much speculation about them and a lot to be debatable.