TITANs are, or perhaps were, seed AIs that became active at some point during the Fall. Some believe the TITANs were responsible for the Fall in the first place. The horrors attributed to the TITANs on Earth, as well as Luna, Mars and much of the rest of the system, cannot be denied. In a few short years, TITAN activity helped to destroy 95% of the human species.
Although their sudden, apparent disappearance marked the end of the Fall, no one is completely sure they’re gone. It is speculated, by some, that the TITANs built the Pandora Gates to make their escape from our systems. Even if they are gone, their legacy lives on in many forms. Earth and other locations are still swarming with the terrible machines and nanoswarm plagues they left behind. The biological remnants of humans and other species transmuted into literal monsters by the Exsurgent Virus continue to be discovered and destroyed.