James got Weezing for Christmas as a Koffing. During the journey in the Kanto Region it became James' Main Battling Pokémon. It was known for blinding Pikachu with Sludge as a Koffing. In the 28th episode, it is used for a clothing advertisement. It was often used by James, sometimes Jessie, as well as Team Rocket's get away escape by using either Smog or Smokescreen. It evolved from Koffing in the episode Dig Those Diglett at the same time Jessie's Ekans evolved into Arbok.
James had to release his Weezing along with Jessie (who had to release Arbok) to save a group of Koffing and Ekans. They strongly cried when they did. Nothing is known of Weezing or Arbok now. They are presumed to still be with the Koffing and Ekans to this day.
Weezing has a strong bond with James, in which James once said that he and Weezing were like brothers. It shows a great deal of loyalty to him, and often shows extreme sadness whenever it is separated, which also shows how emotional it is. While it's love and loyalty is very clear, Weezing, much like Jessie's Arbok, never sees itself or any other Pokémon as bad guys and as Arbok stated in Island of the Giant Pokémon when it was an Ekans and Weezing was a Koffing, they do bad things because their trainers are bad.