Stan Lee, the American comic writer who co-created Marvel superheroes Spider-Man, Thor, The Hulk and the X-Men, died in Los Angeles on Monday, according to The Hollywood Reporter. He was 95 and had suffered several illnesses in recent years.

“He felt an obligation to his fans to keep creating,” his daughter JC Lee told Reuters in a statement. “He loved his life and he loved what he did for a living. His family loved him and his fans loved him. He was irreplaceable.”

Lee was born Stanley Martin Lieber in Manhattan in 1922. At 17, he started writing scripts for superhero and mystery comics at a publishing firm. Two years later, he wrote a two-page story for Jack Kirby and Joe Simon’s Captain America No. 3, using the pen name Stan Lee. The same year, he was named the interim editor after the previous editor quit.

Lee collaborated with artists such as Kirby and Steve Ditko to create a galaxy of superheroes including the Fantastic Four, Iron Man, Captain America, Doctor Strange, Black Panther, Daredevil and Ant-Man. Lee’s world of superheroes expertly straddled books and movies, and his imagination and writing made Marvel a formidable Hollywood franchise.

Disney bought Marvel Entertainment in 2009, and Lee made cameo appearances in almost every Marvel movie. “Stan Lee was as extraordinary as the characters he created,” said Walt Disney Chairman and Chief Executive Officer Bob Iger. “The scale of his imagination was only exceeded by the size of his heart.”

“No one has had more of an impact on my career and everything we do at Marvel Studios than Stan Lee,” Marvel Studios President Kevin Feige said. “Stan leaves an extraordinary legacy that will outlive us all.”

Several celebrities paid tributes to Lee as news of his death broke on Monday morning. “There will never be another Stan Lee,” said Chris Evans, who starred as Captain America in the recent Marvel movies. “For decades he provided both young and old with adventure, escape, comfort, confidence, inspiration, strength, friendship and joy.”