Ganthet describes the creature as "the living light bestowed upon this universe that triggered existence itself". Similar to the emotional embodiments, Predator, Ion, and Parallax, The Entity is the embodiment of life.
In Blackest Night #7, Nekron summons the creature, who had been hidden on Earth by the Guardians of the Universe, by using the entrails of a Guardian. Whenever Nekron hit it, every living being in the universe experienced pain. Hal Jordan surmises that it just took the pain because it did not have a "pilot". Hal rushed to join with The Entity, but was blocked by Sinestro who then bonded with The Entity.
In Green Lantern v.5 #52, Sinestro gets a glimpse of The Entity's history. According to Sinestro, the birth, or entrance into black, endless space, was violent. There is no telling if The Entity was here by accident or with purpose. As the light fought against darkness, stars and planets were born including a planet at the very spot The Entity entered - Earth.
As The Entity's influence spread, life was created and, with life, emotions. As emotions began to manifest, so did the seven emotional embodiments. Before Sinestro could bear witness to more history, he was split into two by Nekron's scythe. Indigo would comment that Sinestro suffered no trauma or damage as she attempted to heal him.
The Entity commanded Sinestro to live, and he was "reborn". He proclaimed himself the true guardian of the universe, and readied himself to attack.
In Blackest Night #8, Sinestro uses the power of The Entity to attack Nekron and rip out his heart. This, however, is not enough to stop Nekron who rips The Entity free from Sinestro. As Nekron strikes The Entity, Hal Jordan pushes through claiming that he chose life. Hal's will combined with his life gives him the power to override the black rings of the undead Justice League of America. The "reborn" League then sets their sights on Black Hand as the force of The Entity then moves on and revives Black Hand. With Nekron's anchor revived, Nekron is weakened as Black Hand coughs up a white ring which revives the Anti-Monitor. Black Hand continues to cough up white rings which destroys Nekron and revives certain people. After the night, Hal Jordan tells Barry Allen that no one knows where The Entity went, but that he still feels his presence urging him to move forward into tomorrow.
In Brightest Day #0, Sinestro finds the fallen white power battery. In Green Lantern v5. #53, he tells Hal Jordan that The Entity is asking for Hal which leads one to guess that The Entity resides in the power battery.
It has revealed in Brightest Day Aquaman #3 that the other reason for the twelve resurrected heroes are because they are needed to prevent the Earth from succumbing to the corruption caused by man and Nekron's attack during Blackest Night. It states that the forest in Star City is the key to Earth's survival and the heroes resurrected must complete their individual missions.
In the Flashpoint universe, an infant version of The Entity slumbers deep beneath the Earth's surface. Concerned for its safety, The Guardians of The Universe ordered Abin Sur to evacuate it from Earth and bring it back to Oa before the Atlantis/Amazon war destroys the planet itself.