Cheren Schwarz

Cheren is a childhood friend of the player who, like the player, lives in the starting town of Nuvema Town. While he holds a greater knowledge in Pokémon than his friends and tends to offer the player advice during the course of their journey, his comments are often witty and intellectual. He also misunderstands Bianca's humor often, to her dismay. Whilst Professor Juniper describes him as being very honest, she also remarks that he can be 'a little difficult'; his impatience in particular is often seen throughout the earlier stages of his journey. He is also described as being quite judgmental by Alder.
In keeping with the theme of truth and ideals often seen in Black and White, Cheren represents those who pursue ideals—more precisely, as N pointed out in Chargestone Cave, the ideal of strength. His goal is to become the Champion and always strives to become stronger- yet the first time that Alder asked him why he strives to become stronger, he was quite unsure of his reasons. He then starts to ponder to himself how to do so—something that Alder said he used to do with his partner Pokémon as well—and what exactly it means to be strong. Alder also remarked that Cheren is a lot like Marshal.
Like the player and Bianca, Cheren receives a starter Pokémon as a gift from Professor Juniper at the start of the game. He always chooses the starter with a type advantage over the player's starter. The player will encounter and battle him several times throughout the game. After the main storyline, Cheren can be found inside Victory Road where he can be battled once a day.

bulbapedia.bulbagarden.net/wiki/Cheren