ELS

Planet of Origin: A planet on  the far side of the galaxy in their old home world. After billions of years of their evolution, their planet was on the brink of destruction as their sun went supernova and engulfed their home world. To survive, they sent out a expedition force in a giant sphere about 3000 kilometers in diameter in search of a new place to settle on/assimilate and make into their home world. Along their expedition, they assimilated and reformed several planets and planetary systems. Their journey ended in the Solar System in the year A.D. 2314, when they arrived near Jupiter and encountered the Europa, a space exploration ship and assimilated it, sending it on a course to Earth. 

The ELS is a peaceful techno-organic sentient species that has the unique ability to assimilate/infect nearly all life and technology.  They appear as silver metallic organisms that can take solid or liquid-like forms. While not aggressive, their ways of understanding their environment is based on assimilation of all things. The ELS has no true form as they are capable of taking any shape or size relative to their mass. They can combine or separate from one another to increase or decrease its mass as needed. When faced with an opponent or something they don't understand, the ELS can assimilate and convert the target of interest into an ELS. 

When confronted with unknown organic lifeforms and/or technologies, the ELS assimilates the target like an aggressive virus. It's rapid adaptability and versatility allows it to take hold of technology in a matter of seconds and organic matter in a manner of minutes. However, for organics, it can have detrimental effects to those not completely assimilated, such as causing brain damage and various biological instabilities due to their invasive nature to their condition. While their complete nature is not understood, it IS understood that they can utilize quantum brainwave frequencies, make copies of what they have assimilated.The ELS also are able to develop countermeasures against enemy forces.

The ELS assimilation process can come in two different ways. One is where a ELS attaches itself to a technological construct or a living organism and stays attached, appearing as large metal shards covering the infected target. The second way is an actual merger with the target, appearing as a mercury-like substance covering the target.

First contact turned into a short war which was followed by the  full merger of a human and the ELS and the ensuing mutual understanding. The ELS began returning to their mothership, now reconfigured into the shape of a desert flower, signifying the end of hostilities. Fifty years later, the  desert flower remained in orbit of Earth, indicating that the ELS maintain a form of co-existence with humanity. 

Source: MS Gundam 00 universe, MS Gundam 00 Movie: A wakening of the Trailblazer