Bill

Bill is the creator of the machine that allow to fusion two Pokemons. He gave one of his fusions to every Gym Leader (excluding LT surge). You first meet him in the Viridian Forest being attacked by a beedrill and he will fight you with a Pikavee (soon after). He will also give you a fusion of your starter and an Eevee(at sea cottage.) His machine will be stolen by Zubats just after that.