Cox is the protagonist of Monster Rancher Explorer and also appears many years later in Monster Rancher Battle Card. Cox is a young student-explorer who is searching for the Phoenix, and becomes famous after unlocking the secrets of the White Tower. A reference is made to Cox in Monster Rancher 4 because the manuscripts in the library in Ryuwn are from his journals.
His laboratory is located in the city of Aurora, where his brother Knox also lives. You can get there by walking to the building to the left of the Battle Card Center. When the Sealed Underground Ruins are discovered during the events of Monster Rancher Battle Card, Cox brings a team of his best researchers to help uncover its secrets.