Osamu Tezuka, who is my manga hero and dubbed by many as "God of Manga" for practically inventing most of the genres of manga seen today in Japan, originally trained as a doctor, but on graduation he decided to become a manga artist instead. Although Astro Boy is his best known production in the west, many in the East, myself included love Black Jack.
The surgeon Black Jack is a miraculously gifted doctor and the stories are a great introduction to many medical conditions, as Tezuka writes and illustrates real disease as only a doctor could. His sidekick, Pinoko was originally a teratoid cystoma, which is where a twin attaches itself in the womb to the other twin and grows. All the organs may still be there, but usually the cystoma is removed and thrown away.
Black Jack saves a cystoma, builds it a body and nurtures it, and it becomes his assistant.
Pinoko usually serves as the light comedy relief in the stories, giving a lighter edge to the stories.