Lugh was a Goa'uld Underlord by System Lord Manannan mac Lir. After he had served Manannan mac Lir so gave him a new status as the Warmaster. But also gave him an even more important asset his queen Morgause. (RPG: "Living Gods: Stargate System Lords") He was subsequently imprisoned and raised his Warmaster of Cuchulainn instead of the first.
Lugh spent the next several years by Mordred trained him in the art of war. With the power vacuum that had been created because of Lugh's death that was quickly filled by Manannan mac Lir and Dagda promoted new General from their Underlord. (RPG: "Living Gods: Stargate System Lords")