Real Crazy Man is the pen name of Park Dong-sun, a South Korean art teacher and the original creator behind the anime and manga series Ketsuekigata-kun! (also known as A Simple Thinking About Blood Type). The creator began the project as a webtoon serialized on a personal blog under the Korean title Hyeoraekyeonge gwanhan gandanhan gochal. The work was subsequently picked up for professional publication in Japan by Earth Star Entertainment, which began releasing compiled manga volumes starting in January 2013.

Real Crazy Man is most widely recognized for Ketsuekigata-kun!, a comedy series that anthropomorphizes the four main human blood types—A, B, O, and AB—into distinct characters. The stories explore the common Japanese stereotype that a person's blood type is indicative of their personality, with Type A individuals being reliable, Type B passionate, Type O independent, and Type AB capricious. The original work is a yonkoma, or four-panel comic, that offers a lighthearted observational look at the daily lives and interactions of these blood-type characters.

The success of the manga led to a television anime adaptation. The first season, also titled Ketsuekigata-kun!, aired in Japan from April to June 2013. Following its popularity, a second season, Ketsuekigata-kun! 2, was green-lit and premiered on January 8, 2015. The anime franchise continued with a third and fourth season, with the final season airing in early 2016. The anime productions were directed by Yoshihisa Ōyama and produced by studios including Assez Finaud Fabric and feel..

The artistic identity of Real Crazy Man is defined by this signature work, which relies on simple, cute character designs to represent abstract personality types. The creator's background as an art teacher is noted in reference sources. The industry significance of Real Crazy Man lies in successfully transitioning a personal webtoon from a blog into a multi-season anime franchise in a foreign market (Japan), demonstrating the cross-cultural appeal of the blood type personality concept. The franchise management and copyright are credited to Leeonsmart Co., Ltd. in conjunction with Earth Star Entertainment.