Cheren

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 yours.

In Pokémon Black/White, Cheren is one of your friends who will encounter on your journey and also battle you after you defeat every gym leader. After you receive your freeze badge, Cheren helps you beat Team Plasma in Dragonspiral Tower and give you useful tips.

In the Manga
Unlike in the game, his starter is weaker compared to the main character.

Black and White
Cheren is a very intelligent boy. His starter will always have an advantage over you and he will very often challenge you to battles.

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. 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 you, sometimes giving you items when you defeat him. His goal, like many other previous rivals, is to become the Pokémon champion. You challenge Cheren right before entering Victory Road, and is then seen with Champion Alder before you face N, and Ghetsis.

After you defeat N and Ghetsis, Cheren appears before your house, where he says that he's 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 he will battle you, just like the old times.He will be waiting for you at the top of Victory Road.

Black 2 and White 2
Cheren will appear in Pokemon Black 2 and Pokemon White 2 as a -type Gym Leader. He serves as a replacement for Lenora and will award the Basic Badge to challengers who defeat him.

First Battle (Nuvema Town)
If User Chose Oshawott/If User Chose Tepig/If User Chose Snivy

Second Battle (Striaton City)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Third Battle (Route 3)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Fourth Battle (Route 4)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Fifth Battle (Route 5)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Sixth Battle (Twist Mountain)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Seventh Battle (Route 10)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Eighth Battle (Victory Road) (After completing main game)
If player chose Oshawott:

If player chose Tepig:

If player chose Snivy:

Black 2 and White 2
In Black 2 & White 2, Cheren reappears as the first gym leader who specializes in Normal type pokemon.

Trivia

 * Currently, despite the fact that Bianca has appeared many times, Cheren has yet to have an appearence in the anime.
 * Cheren is the first rival to wear glasses.
 * He is one of only 3 characters in Black and White to have animated sprites, Bianca and N are the other two.
 * Cheren respects Alder knowing that he is the champion.
 * Despite the fact that he aims to be Champion, he has a Liepard and Unfezant which have been considered very weak stat-wise.
 * His Elemental Monkey matches the type of the player's starter.
 * He looks simaler to Dib from "Invader Zim." Mainly because of his hair and glasses.
 * Cheren is second rival in the Pokemon series to become a gym leader, the other being Gary