He welcomed SG-1 to the planet, after they discovered the use of their Stargate. However, he learned that Soren, a religious leader was attempting to take over Rand and attack the Caledonian Federation. The Caledonians launched a pre-emptive strike to take down their military installations, so the forces wouldn't falter, and left them under the control of Soren.
After he successfully took over the command bunker, Soren had Gareth captured, and executed him and his soldiers. (SG1: "Icon")