The Babylon Project

The "mind-altering aliens" were an unnamed alien species that the Excalibur encountered.[1]

Long ago they found rather than actually attempt to seed the galaxy using traditional means, it was far easier to spread their consciousness into a preexisting species. Their consciousness became the dominant one, repressing the host's consciousness.

Prior to their encounter with the Excalibur in March 2267, the aliens attempted to take over an unnamed alien's ship. They were unsuccessful when the aliens they were trying invade sacrificed themselves in an attempt to jettison everyone, infected or not, into space. One alien was able to put itself into suspended animation, to keep itself from dying. The rest of the infected aliens were able to transfer their consciousness back into one body.

Unaware, the crew picked up the remaining lifeform, which was later able to infect a med-tech, Janey, who then began to infect the rest of the crew one by one. Max Eilerson quickly figured out that the ship had two separate and distinct writing languages on the ship, and that one was completely foreign to the other. The infected crewmen began to descend on Max, who was able to escape from harm, but not before crewman Stewart Greenberg was killed. Eventually a large portion of the crew was infected, with Mr. Welles taking the role as their leader. David Arkham was then killed in a show of force, which spurred Captain Gideon into action.

When Gideon went to meet the possessed people, Eilerson figured out that Gideon wanted them to depressurize the deck, forcing the intelligence back into one person. The alien consciousness was tricked into entering Greenberg's body, which was left available for the aliens to use per Max' suggestion. The body was then flushed out into space and fired upon.

Though not heard by the crew, the last thing that the alien consciousness said before it was killed was "Don't do this! I know what you're looking for!" and "I know where you can find it!"