He's Lady Trieu's Unseen Partner
Another possibility involves Lady Trieu — after all, the show has more than hinted at a connection between them. Trieu is the one who created and controls the satellite booths that link Earth to Mars, and she's also behind the technology the Seventh Kalvary is using for teleportation. We know she bought a blue comet, and Manhattan is the only player we know who is capable of traveling through space. Are they working together somehow? Perhaps Dr. Manhattan changed his mind, imprisoned Veidt in space, and is helping Trieu's plan on Earth.