The Entity (sometimes called The Entity from the Moon) was a fictional device from Malibu Comics' Ultraverse. It first appeared in The Strangers #1; its origins were detailed in Ultraverse Future Shock, Phoenix: Resurrection, Ultraverse: Year Zero, and Break-Thru.
Four billion years ago, an alien spacecraft exploded in the Solar System. The core of this craft wound up on Earth's Moon, while the main body of the vessel crashed on Earth. Over time, the ship's self-repair mechanisms began to activate, and organic nanotechnology began to scour the world for missing pieces of the ship and materials to rebuild what could not be repaired. A few of these molecular machines malfunctioned, and became entangled with other self-replicating molecules that made up the living organisms of this planet.
After four billion years, the starship core on the Moon also began to repair itself, and to seek out the rest of the vessel. It sent out pulses of energy designed to signal the missing vessel; but since every living creature on the planet now contained traces of the same technology, there was an unexpected side effect. In life-forms with a sufficiently complex nervous system (i.e., humans) there developed certain abilities to manipulate matter and energy, and in some cases even space and time. These humans would come to be called "Ultras", and many of them would become quite famous (or infamous) because of their abilities.
The starship core, which would now come to be called the "Entity", reached out to Amber Hunt, attempting to use her to complete its repairs and send itself home. But since the tremendous energy released was dangerous to the population of Earth, several Ultras banded together to shut down the Entity. This event was called Break-Thru, and was the first massive cross-over in the Ultraverse.
In another attempt to reconstruct itself, the Entity began to probe multiple alternate realities and drew the Phoenix Force into the Ultraverse. Once again, it sought out Amber Hunt and made her the receptacle of the Phoenix Force. The various parts of the starship now sought to unite, drawing the Earth, Moon, and the Sun closer together, threatening all life on Earth. Amber/Phoenix, the X-Men, and several Ultras disabled the ship from within, and the Phoenix Force destroyed most of it. However, in the process, the Phoenix Force opened a rift in time, causing the original accident that disabled the ship in the first place.