The face of Marvel Comics, Stan Lee, has died at age 95.

Lee, former editor-in-chief, as well as publisher and chairman, of Marvel Comics, was taken to the Cedars-Sinai Medical Center early Monday morning, where he was pronounced dead. Lee has battled health issues in recent years, including a bout of pneumonia that hospitalized him in February.

The cause of death has not yet been released.

Lee is known for being the co-creator of some of the biggest icons in comic book history. His characters and stories have included Iron Man, Spider-Man, the Incredible Hulk and the X-Men.

Lee has been an enduring figure in the comic book world for over four decades, making many appearances in TV shows as well as cameos in a large amount of Marvel films. Lee was known for his short-but-humorous cameos in nearly every Marvel film. The comic book icon ventured into the industry in the 1950s and has become the biggest name in the art form since.

Lee frequented comic book conventions throughout the country and also gave a number of lectures around the world at colleges and schools. Lee has also been a successful philanthropist through the Stan Lee Foundation.

The foundation’s website describes the charity as “a non-profit organization that seeks to provide access to literacy, education and the arts throughout the nation.”

In 2008, Lee was awarded the National Medal of Arts by former President George W. Bush.

Lee’s contributions to the comic book industry have been widely praised by others in the industry. Celebrities on Twitter showed the writer a outpouring of admiration upon the news of his death.