A small, hunchbacked man with buck teeth. His back can split open to release the poisonous insects that he's developed. He is proud of his "insanity insects", which cause people to lose their memories after being bitten into.

Dr. Mamushi's name refers to the Japanese mamushi (Gloydius blomhoffii), a venomous pit viper. They along with the Okinawan habu (Trimeresurus flavoviridis) are considered to be the most poisonous and deadliest snakes in Japan, where up to 3000 people die from snake bites from a mamushi every year.

His original name, Dr. Semushi, refers to the Japanese word for "hunchback" and reflects his physical appearance, much as the other doctors' names describe theirs. However, due to the term being considered offensive to people with the disability, this necessitated the change to "Mamushi" in later reprints, which may have come about to reflect his poisonous nature, as well as supply a similar-sounding name.