The Japanese publisher Hakusensha announced today that Berserk creator Kentaro Miura died on May 6 of a heart disorder. He was 54.

While Miura created several shorter manga series, Berserk was his magnum opus. The first chapter was published in 1989, and at the time of his death the story was 40 volumes long and still incomplete. It is one of the best selling manga of all time, and the English translation is one of the rare graphic novels to make the best-seller lists in both bookstores and comic stores in the U.S.

Miura was born in Chiba City, Chiba Prefecture, Japan, in 1966 and started drawing manga as a child. His first published work was a doujinshi (fan comic) that friends helped him get published in a magazine while he was still in high school. He became an assistant to Hajime no Ippo manga-ka George Morikawa at the age of 18 and later worked for Fist of the North Star co-creator Buronson as the artist for the manga Orō (published by Dark Horse as King of Wolves). In 1988, while he was still working on that series, he created a 48-page prototype of Berserk that was published in the magazine Gekkan ComiComi and led the publisher Hakusensha to greenlight the full series. Berserk began serialization in 1989 and has been ongoing ever since, although it went on hiatus several times. Miura is also the creator of Japan and Giganto Maxia,both of which were published in English by Dark Horse.

On its official Twitter, Dark Horse offered condolences to Miura’s family and Tweeted, “It has been the utmost privilege of all at Dark Horse to have worked with Miura-sensei over the years. His work inspired countless others to pursue their passions in art and storytelling.”