Hailing from a planet that seemed to be made up of nothing but technology, the creature was sent to earth as a weapon against the SG program. The reason was not malicious but rather due to a terrible misunderstanding by both parties. When Stargate Command sent a MALP through to the planet, as was customary in order to check that the planet was safe to explore, the aliens were at first curious. It was then quickly discovered that the radio waves of the MALP were toxic to them and had caused a tremendous amount of damage before the aliens realized what had happened.
Believing that this was an act of war, the aliens sent an AI weapon back through the gate in order to destroy the supposed invaders. It eventually possessed Major Samantha Carter in order to survive, but when Colonel Jack O'Neill threatened to send an army of MALPs to its world and destroy it, the entity sacrificed itself to protect its world and save Major Carter by transferring her mind to a computer system it had created and allowing itself to then be killed as it could not leave her as O'Neill demanded. (SG1: "Entity")
In 2005, when the Wraith computer virus survived a similar system shutdown to the entity, Dr. Rodney McKay remembered the report on the incident with the entity and how it had survived by uploading itself to a M.A.L.P. McKay realizes that the virus must've done the same thing the entity did, except it uploaded itself to the navigation computers of the Daedalus F-302s. Using this information, they are able to figure out how to destroy the virus. (SGA: "The Intruder")
In 2007, when encountering the Crystal of M3X-387, Doctor Kate Heightmeyer recalls Carter's encounter with the entity. Carter noticeably grimaces and states that it's "not a personal highlight." (SGA: "Doppelganger")