Cheren is one of two friends/rivals the main character has in Pokémon Black and White. All three of them reside in Nuvema Town. He is the rival that picks the Pokémon that has a type advantage against the player.
Unlike in the game, his starter is weaker compared to the main character.
In the games
Black and White
Cheren is a very intelligent boy.
Cheren appears at the beginning of the game as one of the player's friends. He is one of the characters who receives a starter as a present from Professor Juniper. His starter will always have an advantage over the player, and he will often challenge the player to battles.
Since Bianca chose the Pokémon with a type disadvantage against the player's, he has no other choice but to take the Pokémon with a type advantage, though he said he wanted that Pokémon from the start. He later reappears many times throughout the game to battle the player, sometimes giving the player items when he or she defeats him. His goal, like many other previous rivals, is to become the Pokémon champion. The player challenges Cheren right before entering Victory Road and is then seen with Champion Alder before the player faces N and Ghetsis.
After defeating N and Ghetsis, Cheren appears before the player's house, where he says that he is going to explore the region, starting from Route 1.
He can be seen outside of Nimbasa City, where he recalls the day that he met Alder, and how it was the start of his new look on becoming stronger. He then says he will go to the Pokémon League, where the player may choose to battle him once per day atop Victory Road.
Black 2 and White 2
Cheren will appear in Pokémon Black 2 and White 2 as a Normal-type Gym Leader. He serves as a replacement for Lenora and will award the Basic Badge to challengers who defeat him. He also appears often throughout the course of the game to help the player out or to give him or her advice.