L-374 I was the first planet in the L-374 system, which lost two planets in the planet killer attack of 2267. This planet was located in the Beta Quadrant.
When the crew of the badly damaged USS Constellation was unaccounted for after the planet killer's attack, Spock considered it improbable that the ship's crew had fled to L-374 I as this planet had a surface temperature of molten lead (approximately 327 °C). (TOS: "The Doomsday Machine")