The Alsurans were a civilization native to the galaxy's Delta Quadrant. They controlled the Alsuran Empire.
In alternate timelines created by the Krenim temporal weapon ship KIS Kyana Prime, the Alsuran Empire (if not the Alsurans themselves) had been erased from history by the Krenim scientist Annorax to make his native Krenim Imperium more powerful. (VOY episode: "Year of Hell")