A Delta Quadrant power whose scientist Annorax used a temporal weapon ship to rewrite history in its favour.
The Krenim Imperium is a territorial state in the Delta Quadrant that guards its space aggressively and has fought wars with the Zahl and other neighbours. Voyager crosses its territory in the episodes Before and After and the two-part Year of Hell.
In Year of Hell, the Krenim scientist Annorax uses a weapon ship to erase entire species from time in an effort to restore the empire's past glory. The resulting year of attacks leaves Voyager badly damaged, until the weapon ship is destroyed and history is reset.