In 2377 holographic prey created by the Hirogen with Voyager's technology rebelled, killing their hunters and seeking a homeland of their own.
After Janeway gave the Hirogen holographic technology, the Hirogen made their simulated prey smarter and more dangerous. In 2377 the holograms aboard one training facility rose up, killed most of the Hirogen and took a ship. They were led by Iden, a Bajoran hologram.
The holograms took the Doctor, who sympathized with them, and won over the Hirogen engineer Kejal. Iden became a violent fanatic, and the Doctor turned against him. Iden was killed, and the remaining holograms settled on a planet of their own.