Baikinman originates from Baikin Planet, arriving on Earth in an egg that hatched simultaneously with Anpanman's creation. He serves as the primary antagonist across the franchise, driven by an inherent purpose to defeat Anpanman, often declaring, "I was born to defeat you, Anpanman!" His core motivation stems from this oppositional role, though he occasionally demonstrates reluctant cooperation when Anpanman faces unrelated threats.

Physically, Baikinman resembles an anthropomorphic fly or bread mold germ (Rhizopus stolonifer). He possesses a black furry body, fly wings, a zigzag tail, purple lips and nose, light pink eyes, a slimy blue tongue, and large teeth. Exposure to soap or cleanliness triggers a severe allergic reaction, causing his body to turn white and shrink.

His personality is defined by narcissism, impulsiveness, and rudeness. He frequently praises himself, resides in a self-shaped castle, and exhibits gluttonous tendencies, often attempting food theft. Despite proclaiming himself a loveless genius scientist, he displays unexpected complexity: creator Takashi Yanase indicated Baikinman harbors latent desires for a normal life, constrained by his destined role. He engineers elaborate robots and machines for his schemes, though these frequently fail.

Key relationships shape his actions:
- **Anpanman**: Their rivalry is existential, yet Anpanman persists in offering friendship. Their shared birth date creates an unspoken connection.
- **Dokin-chan**: As his frequent partner, Baikinman harbors unrequited romantic feelings, complying with her demands despite her preference for Shokupanman.
- **Franken Robo-kun**: A robot he created views him as a father figure. Baikinman exhibits a reluctant soft spot for him, though he avoids physical contact due to the robot’s electrocuting hugs.
- **Rollpanna**: Baikinman implanted her with a "Baikin Plant," creating her blue evil heart to control her against Anpanman. This influence remains inconsistent, as Rollpanna often defects to aid heroes.

Baikinman's design draws inspiration from Beelzebub, the demonic "Lord of the Flies". This influence extends beyond the franchise; a Pokémon episode depicted computer viruses resembling him. The character Vaccine Man in *One Punch Man* parodies Baikinman and shares his Japanese voice actor. As one of the most persistent figures in the series, he appears in nearly every episode, embodying relentless resilience despite repeated defeats.