From Bulbapedia, the community-driven Pokémon encyclopedia.
Nelson (Japanese: ナオヤ Naoya) is a young Pokémon trainer from Johto who dreams of catching Entei. He was the character of the day in Entei at Your Own Risk. His Japanese voice actress is 沢海陽子 Yōko Sōmi and his English voice actress is Kayzie Rogers.
He set up a complicated series of tripwires and alarms to detect where Entei would appear, then used his laptop to monitor them. However, the traps ended up capturing Ash and his friends instead of Entei. Eventually, Entei appeared when Team Rocket nearly destroyed the hot springs.
Nelson's strategy was to use Mean Look to trap Entei so he could capture it, but didn't realize that Entei's Roar would cancel out his Mean Look. After discovering this, it only added to Nelson's desire to capture the Legendary Pokémon.