Ditko was found dead on June 29 in his midtown Manhattan apartment, New York Police Department spokesman George Tsourovakas told CNN.

Marvel President Dan Buckley said in a statement "the Marvel family mourns the loss" of Ditko.

"Steve transformed the industry and the Marvel Universe, and his legacy will never be forgotten," Buckley said. "Our thoughts are with his family, loved ones, and fans during this sad time."

Jim Lee, publisher of DC Entertainment (home to Batman and Superman), said in a series of tweets that while Ditko was known for co-creating Spider-Man, he did work on the DC side as well.

Sad to hear of the passing of the legendary artist and creator Steve Ditko. Beloved for generations-- his work was the Quirky to Kirby's Majesty and helped provide the early visual vocabulary in counterpoint to Kirby's power and influence. 1/3 pic.twitter.com/GvH8Mcrxg6 — Jim Lee (@JimLee) July 7, 2018

"He also ushered in a slew of unique, very personal and eclectic characters for DC such as the Question, Blue Beetle, Hawk and Dove and more," Lee said. "Polite and unassuming -- he never sought attention or the limelight but in many ways represented the hidden hero he saw in all of us. #RIPsteveditko"

Of course, he is best known for co-creating Spider-Man but he also ushered in a slew of unique, very personal and eclectic characters for DC such as the Question, Blue Beetle, Hawk and Dove and more. I only met him once back in the hallways of Marvel when I worked there. 2/3 — Jim Lee (@JimLee) July 7, 2018

Polite and unassuming--he never sought attention or the limelight but in many ways represented the hidden hero he saw in all of us. #RIPsteveditko 3/3 — Jim Lee (@JimLee) July 7, 2018