Tatsuo was born into a rich family. His parents were scientists they created a protector for their son named Garo who could turn into a wolf, bat, crocidle monster. They were killed by his grandfather due to thinking Tatsuo was one of their creations. Garo saved him and gave him to the Kagura family who raised him. Years later still remebering what happened to his parents he beacame the Skull Man. Him and Garo killed anyone responisble for his parents death usually resulting in bystanders getting killed in the crossfire. He finally finds who killed his parents and learns he has a sister. His grandfather then set fire to the building resulting in their deaths. Years later Tatsuo and his sister somehow survived the fire. He now is finding allies to join him into finding out who is creating mutants.
Tatsuo Kagura was subjected to several mutating science experiments that ended up giving him amazing powers and skills. Tatsuo planned revenge on the man responsible for his condition: Rasputin. On his adventure Skull Man teams up with his shapeshifting ally Garo. During his crusade Skull Man faces multiple enemies and monsters.
In 2007 an anime adaption was made by Studio Bones. It follows a reporter named Hayato Mikogami and his encounters with Skull Man. As the story progresses Hayato comes closer and closer to the truth who Skull Man is. After seeing the truth, realises there is a more dangerous threat watching over the city.
This version of Skull man is much more darker, grittier and mysterious. It has been hinted several times that he isn't even human. The character is constantly seen with glowing red eyes and daggers. He is always lurking in the darkness wtaching with his glowing red eyes and quoting Nietsche and Macbeth.
Hayato Mikogami returns to his hometwon Ootomo to investigate the rumors of a killer wearing a Skull mask who kills civillians in the night. When he arrives in town he befriends a teenage photgrapher named Kiriko. Skull Man is a mysterious figure who only appears at midnight to kill people. Little does the world know that these innocent civillians are actually mutants who are controlled by the residential cult called the Byakureikai cult. The people have the ability to turn into mutants throught the use of a silver hanger and the drug they have been taking provided by the pharmaceutical company.
Over the course of the story Kiriko and Hayato become more and more entangled in the whole ordeal. The people they can trust and confide in are dwindling. One of the few people Hayato can confide in is his childhood friend turned priest Yoshio Kanzaki. Yoshio has been sent to war zones and there he has faced the ver destructive nature of humankind. Towards the end of the series it's revealed that Yoshio is actually Skull Man, and that the Skull Man’s true purpose is to keep the executives of the pharmaceutical company’s power in check and dish out divine punishment to keep the citizens grounded.
The executives sent out cyborg soldiers to deal with the Skull Man. The battle was long and brutal and during the fight Yoshio is mortally wounded. As he lays dying in the arms of Hayato, Yoshio shows remorse for killing the people. After Yoshio passes away Hayato takes up the identity of Skull Man to stop the cult. He heads for the main building and faces of against a giant mutant. The mutant used to be the stepson of Gozo Kuroshoi and was created by using Maya Kuroshio. Maya is the daughter of Goz and is deeply involved with the cult and is also the woman of Yoshio's affections. When Yoshio took up the Skull Man identity he had to kill the woman he loved, something he reluctantly planned.
In his battle against the mutant Hayato is aided by Gozo Kuroshoi. During the battle he is killed and asks for Skull Man to save his daughter. The mutant and Skull Man face off in an epic showdown. In a flash the outcome is determined, both fighters have been badly wounded. The mutant dies on the spot while Hayato still has a few moments to live. He slowly walks toward Maya and reluctantly kills her, with her dyring breath she reveals that Hayato was her brother all along. The end scene shows Hayato watching over the destroyed city while sun rises. He finally sees what Yoshio saw and then passes away.
The epilogue is set some time after the end. The people Hayato had befriended during his adventure have gone on with their lives. We see Kiriko holding her child who looks a lot like Joe Shimamura the protagonist of another one of Ishinomori's works Cyborg 009. It has been hinted that Hayato is the father of the child. Kyōichirō Tachigi a private investigator in his 50's is one of the people Hayato befriended. He is talking about what could have happened with Hayato. He suggests that Hayato could have been Tatsuo Kagura. When Kyochiro is walking over street he sees Hayato who quickly kills the elderly man.
After that we see the members of Brain Gear another organisation which is featured heavily in the show, who are ushering in a new member. The member has been revealed to be Hayato with a black version of his Skull mask. He swears allegiance to the Black Phantasms. In his Black Phantasms outfit he looks a lot like the main antagonist of Cyborg 009 the Black Ghost. The end hints that Black Ghost is actually the father of Cyborg 009.