NOS-4-A2 was a robot energy vampire created by Evil Emperor Zurg. He fed off of other robots and machines like a vampire, and could take control of them with his mental powers. He was also capable of flight and firing bolts of energy.
He infiltrated Star Command and took control of the robot Space Ranger XR, and the rest of the station in the process. He almost defeated Buzz Lightyear but was beaten by XR when he managed to break NOS-4-A2's mental hold over him.
NOS-4-A2 next went to Cosmo's Diner, taking over the restaurant's new K-3000 Uni-Appliance and using it to assimilate the entire space station. Team Lightyear, armed with plant-based technology provided by Professor Triffid, were able to defeat NOS-4-A2.
The robot vampire later went to Tradeworld, where he began feeding off of robots and converting them into his followers, and was hunted by a self-titled vampire-robot-slayer named Savy SL-2 (a human who was raised by robots). Team Lightyear allied with Savy and defeated NOS-4-A2 once more.
NOS-4-A2 later bit Space Ranger Ty Parsec and changed him into the Wirewolf. He joined forces with XL, and journeyed to Planet Z. After desposing Zurg, he built a giant cannon to infect the entire galaxy with Ty Parsec's condition, turning everyone into Wirewolves existing only to feed NOS-4-A2. Team Lightyear battled him, and conviced XL to change sides once he realized that NOS-4-A2 intended to feed off of him as well. The cannon was destroyed, and the Wirewolf attacked NOS-4-A2, impaling him upon a piece of debris which caused the energy vampire to explode. NOS-4-A2 seemingly perished.