Prior to the start of the series, Green owned Granbull as a Snubbull. She traded it to Silver in exchange for his Horsea after they escaped the Masked Man. Sometime before the Yellow chapter, Silver returned Snubbull to Green.
Tad first used his Poliwrath to battle against Ash and his Pikachu. Before the battle, Tad explains that the reason Poliwrath is wearing a belt is because at his hometown, Poliwrath won against all the Pokémon there and was awarded the belt (though it's unknown if Tad made the belt, or the town gave it to him). The battle then begins with Pikachu using Thunderbolt and Poliwrath dodges with Double Team. Ash then commands Pikachu to use Quick Attack on all the copies then electrocute the real one, however Poliwrath is still in perfect condition. Poliwrath then uses Hypnosis, which causes Pikachu to fall asleep. This leaves it open to a Water Gun attack, knocking Pikachu out.
Ash then sends out his Charizard, only for it to not listen and fly above the water. Tad the commands his Poliwrath to use Water Gun on Charizard, which causes it to come back on the island and after an argument with it's trainer, Charizard uses Flamethrower on Poliwrath. However it still looks like it took no damage at all, and after three Water Gun's, the third one hits leaving Charizard open to an Ice Beam attack, trapping it in ice until Ash can defrost it.
The next day, Tad and Ash had a rematch using Poliwrath and Charizard respectively. Poliwrath starts the match with Water Gun with Charizard dodging and using Ember, Poliwrath then uses Water Gun to destroy the Ember. The two go head to head with Charizard using Take Down and Poliwrath using Mega Kick. After Charizard dodges another Ice Beam, it uses Seismic Toss which causes Poliwrath to faint, ending the rematch.
Very little is known about Poliwrath's personality, but it followed it's masters commands with no problem, showing loyalty. It's also shown to be very strong in battle, as it defeated all the Pokémon from Tad's home town, but it can be beaten.