Rival (originally ???), an NPC, is the archenemy of the player. Rival's goal is to become the greatest Pokémon trainer in the world. He always steals the Pokémon who's type is strong against the player's.
Rival is first seen looking into Elm's Lab, where he is plotting to steal a Pokémon. Upon being noticed by the player, Rival kicks him/her away. Later, on the way back from Mr. Pokémon's House, the player runs into, and battles him. After returning to Elm's Lab, the player can re-name Rival to any name they please.
After getting to the top of Sprout Tower, the player learns that Rival has easily defeated Elder Li, and claims that he only cares for strong Pokémon.
He is next encountered near the exit from Azalea Town where he will want to battle.
The next time he is seen is at the Burned Tower where he is looking for evidence of the legendary Pokémon. After battling him he makes fun of the player when they fall into a hole to the basement.
Shortly after that he will be encountered leaving the Olivine Gym, complaining about the absence of the Gym Leader, Jasmine. He will also mention hearing about a trainer in Cianwood City who has a rare Pokémon. After this a man can be found in Cianwood scared of having his last Pokémon stolen by the same boy who stole his other Pokemon. The boy's description is similar to the Rival and in the next battle he will appear to have gained a Sneasel which isn't available til after that point.
He then shows up at the Team Rocket Hideout where he complains about getting a lecture from Lance about treating his Pokemon better.
After that he will battle in the Underground Path. Afterwards he talks about what Lance told him but still rejects it.
His next encounter is a battle at the end of Victory Road. He claims to have beaten all of the other trainers in the cave(this is verified by the last trainer before the League Gate on Route 26). After beating him, he starts actively thinking about what Lance told him and then leaves to train more.
He isn't seen again until he appears at the Memorial Pillar to help defeat two Team Rocket Grunts and obtain a password for the Rocket Warehouse.
Talking to Rival on Test.