Chet (Mario Tennis: Power Tour)
From the Super Mario Wiki
Chet is a non-playable character in Mario Tennis: Power Tour. He is one of several human characters created exclusively for the Mario Tennis series. He is from the Factory school. His doubles partner is Sass, and he can only be found during the Island Open Doubles Tournament. If talked to, he worries about Sass not being very good in double matches, and says that he has to work doubly hard. He and Sass are knocked out in the first round of the tournament by Dweezil and Mynx. He later complains about Sass's lousy skill being the reason for them losing. Because he is never faced by the player, he can never be unlocked as a playable character.