In a 2020 interview with IGN, series creator Toru Iwatani revealed that the ghosts Inky, Blinky, Pinky and Clyde, were inspired by the Japanese manga "Little Ghost Q-Taro" and the American cartoon character "Casper the Friendly Ghost". More interestingly, he revealed that the ghosts were conceived to always be ghosts, meaning that they never died to become ghosts, and are more akin to Yōkai in Japanese culture as "ethereal beings and concepts that reside among nature that were simply 'there' from the very beginning."
Contributed by MehDeletingLater