Santos was a member of the Maquis on a settlement in the Demilitarized Zone.

In 2370, he kidnapped Ro Laren and took her to be questioned by himself, Kalita, and Macias to determine if she was a potential Maquis, or if she was a Federation spy. Afterward, he checked with his Federation sources, and believed she was not a spy.

Some time later he was the squad leader in a Maquis attack on an Yridian convoy, which was actually a Federation trap. Luckily, Ro betrayed the Federation and saved the lives of the squad by revealing a Starfleet attack force hidden in a nearby nebula. (TNG: "Preemptive Strike")