Erika's Nidoking is the fifth Pokemon she obtained. He was caught as a Nidoran in A Nidoran in Your Pocket.
Nidoking first appeared as a baby Nidoran trying to climb into Erika's pocket and because of that, she caught him. He helps her win gym battles and dreams of riding in her pocket. He was captured by Team Rocket along with Anna's Nidoran whom Team Rocket was planning on taking both Nidoran to the boss for a big payment. But Erika and Anna rescued their Pokemon and sent Team Rocket blasting off. Erika and her Nidoran are unstoppable and often win Pokemon showcases. During a dance party, Nidoran evolved into Nidorino. During the second season of the Kalos Adventures series, he evolved into Nidoking.
Nidoking as an Nidoran had a playful personality as he enjoyed trying to climb into Erika's pant's pocket, but always ends up being placed on the ground after being told he can't fit in her pocket, but he still dreams of riding in her pocket and often tries to get his wish to come true. Erika loves her Nidoran very much and takes good care of him even protecting him from Team Rocket. Nidoran loves Mint Chocolate Chip Ice Cream and he loves coffee. After he evolved, he became a more mature Pokemon and stopped trying to climb into Erika's pocket. He now takes her seriously as he lost his playful personality. When he evolved into Nidoking, he refused to obey his trainer at first as he didn't recognize her. But when Erika saved him from Team Rocket, he remembered her as his trainer. He now performs in showcases with Erika and the rest of her Pokemon. He is the last Pokemon to fully evolve in Erika's party.