Automated Unit 3947 was a Pralor robot rescued by B'Elanna Torres who forced her to build a prototype so his kind could reproduce.
Automated Unit 3947 was one of the robots built by the Pralor to fight a war against the Cravic. When the two peoples made peace and tried to deactivate their machines, the robots destroyed their creators and kept fighting. With no one to repair or build them, the Pralor units were slowly dying out.
In Prototype, B'Elanna Torres revived 3947 after Voyager found him drifting in space. He asked her to build a power module that would let the robots reproduce, and when Janeway refused, he abducted Torres. She completed the prototype under duress, then destroyed it once she realized it would tip the endless war.