Rival (ライバル Raibaru) is a Trainer Class in the game that battles the player often throughout the main storyline. A rival in the game can be a childhood friend of the player (in the case of Blue, Trace, Cheren, Bianca, Barry, Hugh, and Hop), a recently-met neighbor (in the case of May/Brendan, Wally, Serena/Calem, Shauna, Tierno, Trevor, Hau, and Marnie), or an antagonist (in the case of Silver, Bede, and to a lesser extent, Blue). When the player is choosing a starter Pokémon, the rival will usually get the type that is strong against the player's Pokémon. For example, if the player chooses a Grass-type Pokémon, then the player's rival will pick up a Fire-type Pokémon. The exceptions are Dawn, Lucas, Bianca, Shauna, Hau, and Hop who all choose the Pokémon with a type disadvantage. Wally starts out with a Ralts, rather than a conventional Hoenn starter.
Also, the player can sometimes give their rival a name. The names of the rivals that cannot be named are: Wally, Brendan, May, Cheren, Bianca, Shauna, Calem, Serena, Tierno, Trevor, Hau, Gladion, Hop, Bede, and Marnie.
In the game
Having a rival as the player's opponent was introduced in Generation I with the popular rivalry between Blue/Green* and Red. A rival usually appears in the main game series throughout the game challenging the player to Pokémon battles. Rivals mostly appear early in the main story line. Their starter Pokémon are usually the one that has a type advantage against the Pokémon that the player has chosen, for example: If the player chose Charmander, the rival will choose Squirtle, because Water is strong against Fire. Some exceptions are Bianca, Hau and Shauna who choose the starter that is weak against the player's. Most of the player rivals depend more on strength than strategy.
Semi-rival (半ライバル hanraibaru) is a rival who is more than a Pseudo-Rival but less than a Rival. They will battle the player, but much less frequently than a full Rival.
Pseudo-rival (擬似ライバル Giji Raibaru) is one of the main protagonists from the main Pokémon video game series. They are seen as a helping hand in bringing useful information, giving useful items and helping during tag battles. They are seen as rivals in being more in a competitive manner in completing the Pokédex instead of participating in Pokémon battles.
In the anime series, many rivals for the main characters has been appeared. The rivals in the anime can be compared to that in the video games. The main characters also learns a lot from their rivals during their competitions. Even some of the main characters Pokémon have their own rivalry with other Trainer's Pokémon as well. Known rivalries in the series:
- Known is that Ash has a lot of rivals during his travels, but his major rivals were: Gary Oak, Paul, Trip, Alain and Gladion — with the first 3 once unfriendly to Ash. Gary was a rival during Kanto and Johto, Paul during Sinnoh, Trip during Unova, Alain during Kalos and Gladion during Alola.
- Ash also had a lot of minor rivals in the anime series. However, they are mostly more in collecting badges and holding friendly battles, which some of them achieved in competing with each other in the Pokémon League. Prominent minor rivals include Ritchie in Kanto, Harrison in Johto, Morrison and Tyson in Hoenn, Barry, Conway, Nando and Tobias in Sinnoh, Bianca, Stephan, Cameron and Virgil in Unova, Sawyer, Tierno and Trevor in Kalos, and Kiawe, Hau and Masked Royal in Alola.
- Jessie and James both have a rivalry with Butch and Cassidy. Jessie has a major rivalry with Cassidy since childhood, the rivalry between James and Butch can be because of the times that they were assign to capture a red Snorlax, as James was chosen as Jessie's last-chance partner due to a history of not getting along with the preceding ones while Butch (whose name is always mispronounced to his annoyance) got along with Cassidy easily. Butch and Cassidy are both popular and Mid-Class Agents, while Jessie and James are both losers and Low-Class Agents.
- May has a rivalry with her fellow coordinators Drew, Harley and Solidad.
- Dawn has a rivalry with her fellow coordinators Zoey, Nando, Kenny and Ursula.
- Iris has a rivalry with Georgia.
- Cilan has a rivalry with fellow Connoisseur Burgundy. Cilan is an A-class, while Burgundy is only a C-class (which is the beginner and an assistant to A-class and S-class).
- Serena has a rivalry with Miette and friendly rivalries with Shauna and Nini.
- Sophocles has a rivalry with Horacio. Both of them have Vikavolt and they competed on making their Pokémon stronger.
- Ash's Pikachu has a rivalry with its evolve form, Raichu, because of its first fight against Lt. Surge's Raichu. Unlike Team Rocket's Meowth, Pikachu is willing to work with a Raichu, as seen during the Summer Camp arc of the Diamond and Pearl series.
- Ash's Pikachu also has a rivalry with Paul's Electivire (even when it was an Elekid, and Electabuzz), both of them are Electric types.
- Ash's Pikachu had a rivalry with a Sunglasses Krokorok (even when it was a Sandile). Krokorok believed he was superior to Pikachu, due to type advantage. It had been following Ash and the others to battle Pikachu again. After it lost to Pikachu for the last time, it ended its rivalry with Pikachu and agreed to joined Ash.
- Ash's Pikachu has a rivalry with Jessie's Mimikyu. Mimikyu harbors great hatred against Pikachu and its kind will stop at nothing to take him down.
- Ash's Snivy has a rivalry with Iris' Emolga, both of them are females, and Emolga is a mischievous Pokémon who likes to be naughty, while Snivy watches her to stop her mischief.
- Ash's Greninja has a rivalry with Sawyer's Sceptile (even during their evolution lines). Both them are Starter Pokémon and Greninja's powers of Bond Phenomenon rivals the powers of Sceptile's Mega Evolution.
- Ash's Greninja has a rivalry with Alain's Charizard. Both them are Starter Pokémon and Greninja's power of Bond Phenomenon rivals the powers of Charizard's Mega Evolution, which causes their trainers to have their own rivalry because of Greninja.
- Ash's Incineroar has a rivalry with Professor Kukui's Incineroar, Ash's Incineroar want to become stronger than Professor Kukui's Incineroar and won't stop until he defeats him (even when Ash's Incineroar was a Litten and Torracat ).
- Serena's Pancham and Clemont's Chespin has a rivalry with each other.
- Dawn's Piplup and Ash's Oshawott has a rivalry with each other. both of them are Water type Starter Pokémon and had a crush for Meloetta but they finally make amends with each other.
- Meowth has a rivalry with its evolve form Persian (including Giovanni's), mostly because of the fact that the Persian is Giovanni's favorite (which Meowth dislikes because, according to his stories, he was the former favorite of Giovanni).
- Tyson's Meowth has rivalry with its evolve form Persian, because its story of battling a Persian in a snowing forest and lost the battle.
- Tyson's Meowth has an unfriendly rivalry with Team Rocket's Meowth, Tyson's Meowth called Team Rocket's Meowth a pathetic and embarrassment to other Meowth. Both of them shared the pain for their hatred toward their evolve form Persian.
- Ash's Rowlet and Ash's Incineroar have a rivalry with their evolutions(Hau's Decidueye and Professor Kukui's Incineroar respectively. The latter 2 have more antagonistic rivalry than the former 2.
- Gladion and Hop are the only rivals who have a Legendary Pokémon.
- Ash has at least one species of Pokémon from the same evolutionary line as each of his major rivals.
- In every generation, at least one of the player's rivals can be battled at the Pokémon League and/or Victory Road.