You are talking about Kreon of Tebis, Green Lantern of Sector 2002. (DC Database entry here.)
Kreon was one of the "temporary" Green Lanterns recruited by Hal Jordan before he went crazy and killed anyone in his way to Oa during Emerald Twilight. Wikipedia says "At one point, he was described as one of the greatest and most decisive war leaders in the universe. His signature trait as a Green Lantern was that his ring never showed a beam; his constructs were simply 'on' and 'off', suggesting that his mind apparently moved quite fast."
Kreon was depowered by Hal Jordan, then taken by the Manhunters to Biot to power a series of stolen power rings. Kreon died when Hal Jordan attempted to revive and rescue the Lost Lanterns months or years later.