From Bulbapedia, the community-driven Pokémon encyclopedia.
Chris (Japanese: クリス Chris) is a character of the day who appeared in The Mystery of the Missing Cubchoo!. He appeared before Ash and his friends while trying to find his lost Cubchoo. They offered to help look for it, with Cilan finding it to be the perfect opportunity to become a "Detective Connoisseur".
Chris explained that he had last left Cubchoo in the Pokémon House when it went to sleep for the night. When he arrived the next morning, Cubchoo was gone. During their search, the group came across a wild Beartic, which Cilan assumed kidnapped his Cubchoo. That story soon changed to Beartic actually evolving from Cubchoo. When Chris attempted to return it to its Poké Ball, it failed to work, though, indicating it was just a wild Beartic.
The group soon spotted Chris's missing Cubchoo playing with a wild Larvitar. It had helped Cubchoo escape the Pokémon House by opening the door and digging a hole under the fence. Chris realized how close Cubchoo and Larvitar were, so he decided to add Larvitar as a member of his team.