Skull Man was one of manga's first anti-heroes, someone who would sacrifice the lives of innocents in his quest for vengeance.
While the TV series Kamen Rider (Masked Rider) was still in development, Ishinomori, who created that series with producer Toru Hirayama, made this manga as his own personal version, which the producers at Toei Company Ltd. used as the basis for the show. Several changes in content were made, as this 100-page one-shot story was too dark and gruesome (even cerebral) for a children's show.
(Source: Wikipedia)