Stan Lee passed away before he could record any lines for the character "Stan". His likeness was retained for the character's look, but the voice done by Adam Diggle instead.
This is Arnold Schwarzenegger's second time voice acting in an animated television series. His first was an appearance in the 2002 PBS animated TV series Liberty's Kids as historical figure General Friedrich Von Steuben.
Stan Lee originally came up with the idea for Superhero Kindergarten in 1990 as a follow-up to Kindergarten Cop (1990).