Stan Lee has broken his silence following the news that Steve Ditko — the reclusive comic-book titan with whom he co-created Spider-Man and Doctor Strange — died at the age of 90 last month.

In a touching video posted to Twitter, Lee acknowledged Ditko’s passing and paid tribute to his legacy. “I cannot let the week go without commenting on Steve Ditko,” Lee said. “Steve was certainly one of the most important creators in the comic book business. His talent was indescribable.”

In the ’60s, Lee and Ditko collaborated at Marvel to create some of pop culture’s most enduring comic book characters, from the web-slinging Spider-Man to the cosmically gifted Doctor Strange. Ditko was responsible for many of the most iconic details we today associate with Spider-Man, from his web-shooters to the red-and-blue costume. The artist also had a knack for creating colorful adversaries, and was responsible for (among others) Doctor Octopus, the Green Goblin, and the Sandman.

“I worked with him for many years and was always impressed with how he saw everything in terms of photos and pictures and movement and scenes,” said Lee. “He told a story like a fine movie director would.”

The pair had a contentious relationship, and Ditko left Marvel in 1966 after co-creating Strange. He continued working in the comic book industry for decades after, often pursuing characters over whom he could exert more exacting creative control than he’d been able to at Marvel, where Lee oversaw him.

“I’m sure there will be a lot written about him as time goes by and I will be one of the guys who buys the first book. You made a real impression here in the world,” concluded Lee in the video. “Excelsior!”