Black Jack is the manga series from the creator of Astro Boy that is most popular among adult readers.
I don't know what that really means. These stories of a mysterious surgeon, a young man whose hair is part white and part black and whose faces is marked by a diagonally stitched scar, are perhaps somewhat more sophisticated than some of Tezuka's other work, but there is nothing particularly adult about them. Black Jack is an unlicensed surgeon who charges outrageously high fees and insists on working alone in the operating room. He accomplishes the seemingly impossible, and he is not above a certain level of deception. In this first volume we get his back story -- he own hopelessly shattered body was saved by a remarkable surgeon. We also learn that the one true love of his life has been forced to live her life as a man since he removed her womb when she had cervical cancer. These stories were written in the 1970's, so that bit of biological determinism is completely indefensible as a sign of its times. Jack's assistant is a little girl with the mind of a young woman. She was a vestigial twin rescued from the body of an 18 year old. She is also quite irritating.