Spider-Man co-creator Stan Lee died mere weeks before the release of Spider-Man: Into the Spider-Verse. The filmmakers knew they had to dedicate the film to him, which they did at the very last minute, but that was a fraction of Lee’s presence in the film.
Source: io9 – Stan Lee Has a Blink-And-You’ll-Miss-It Second Cameo in Spider-Man: Into the Spider-Verse