Mister serves as Ken's faithful canine companion, consistently joining Ken and Bumboo on their global adventures. He travels alongside them as they journey across the world in pursuit of Bumboo's missing mother; in certain regional versions, the character bears the name Mopsy.

Actively participating in events with Ken and Bumboo, Mister contributes to their exploits. This includes a specific incident where the trio encounters a farmer abusing his donkey. During this encounter, Mister collaborates with Bumboo to simulate haunting the farmer, aiming to reform the farmer's cruel behavior. He remains a steadfast presence throughout the entire journey, confronting every challenge and adventure the group faces together.