A former associate of Vala Mal Doran, Caius is smuggler who hid out in a monastery dedicated to the Goa'uld Grannus, posing as a faithful monk. Vala visited the monastery hoping to reacquire the centerpiece that she had traded to them, a cargo ship's power coil venerated as the Ring of Shen-Marak.
The object was the only thing that kept the monastery alive with the revenue that it helped to generate, Caius told her, and if he was going to return it to her he fully intended to leave. He was tired of bathing the poor and weaving prayer baskets. He agreed to return the coil to Vala's possession, but only if she would return his modified cargo ship to him.
Unfortunately the cargo ship was now in the possession of Tenat and Jup, associates of the Lucian Alliance. But Vala and SG-1 managed to make off with it, trading the vessel for the power coil. Caius presumably then left the monastery and returned to the life of an expert smuggler.
The Ties That Bind - Vala seeks out Caius in the monastery of Grannus, hoping to reacquire the power coil that the monks now venerate.