Gernot, you're thinking of "Earth-D", from "Legends of the DC Universe: Crisis on Infinite Earths, the Untold Story" (February 1999). See this annotated summary:
http://www.io.com/~woodward/chroma/cr4_5.htmlCaptain Jose Hernandez (formerly of the Brazilian Air Force) was the Green Lantern of Sector 5134 (Earth-1 was in Sector 2814) for only a few brief hours before he was slain by a shadow demon and Earth-D died. Yet he had some of the best lines -- questioning Firestorm over the naming of Earth-1 ("Somewhat egotistical, isn't it?" Firestorm's response: "Don't blame me -- I didn't name it!"), and a sobering realization:
"I'm the new Green Lantern!
"My first mission is to save the universe from destruction.
"What will the Guardians expect for an ENCORE?" :shock:
Sadly, Capt. Hernandez never had a chance for that "encore", and he didn't save the Earth-D universe. But his dying act saved Supergirl, who would later destroy the Anti-Monitor's machines that were merging the five remaining Earths. Without Kara, Superman might well have been killed by the Anti-Monitor and the last Earths destroyed, so in a sense the Green Lantern of Earth-D DID fulfill his mission, though not in a way he (or Earth-D) would have preferred...