This Weezing is a poison-type Pokémon owned by James.
He got him for Christmas as a Koffing. During the journey in the Kanto Region it became James's 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 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.
His Weezing helped James capture and defeat Victreebel when it was a Weepinbell in a flashback.
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.