The Marvel Universe is mourning the death of an icon. Stan Lee, creator of the modern day comic book, died Monday at Cedars-Sinai Medical Center in Los Angeles.

As the top writer at Marvel Comics and later, as its publisher, Lee revived and modernized the comic book industry in the 1960s, creating Spider-Man, the Hulk and the X-Men, which has formed part of the monolithic Marvel Universe film franchise. His career there began in 1941, at the age of 17.

Stan Lee’s final tweet was Sunday:

Lee was known for making several cameo appearances in Marvel Universe films, the most recent being Black Panther, Avengers: Infinity War, Ant-Man and the Wasp and most recently Venom, starring Tom Hardy.