He was portrayed by actor Noah Emmerich.
Nelec is the leader of an elite Air Force unit. In 1958, a spaceship crashed and was brought to Area 51. The pilot, known as Cooper, was subject to torturous experiments by Nelec for 20 years. As Cooper and the cubes that made up his ship were being transferred to Hanger 18, a former scientist, Thomas Woodward, drove his truck into the train, derailing it and allowing him to escape. Nelec arrives to secure the crash site while the kids flee the scene. Nelec ends up finding the empty box of Charles' Super 8 film reels, realizing that someone potentially filmed the crash. Using a code word he overheard in the transmissions, Jack tries to get Nelec to divulge what is really happening to the town, but his plan backfires and Nelec has him arrested when he later goes to meet with Nelec in private. Then, Nelec kills Woodward, despite promising he would be safe, and orders his men to start a fire, forcing the townsfolk to evacuate while he hunts for Cooper.
Later in the film, Nelec and his men storm the middle school and capture the boys. They place the boys on a security bus and head back to the Air Force base, but Cooper attacks the bus on the way. Nelec's men are killed, while Joe and his friends escape, Nelec tried to fight Cooper off but he is no match for it. Cooper looks right at him, Nelec froze in fear as the alien exacted vengeance by biting off his head in one attack before leaving the wreaked bus.