>>98828056>A running gag among Tezuka's different mangas was making random characters pop out from nowhere for no reason at all.
It was less of a running gag and more like Tezuka's gimmick. He had this concept of a "Star System" where the characters are all actors playing a role. That way, he can recycle all of his characters and put them into different stories and situations outside their own series. Most of his characters filled a specific archetype. Hamegg and Lamp are commonly used villains, Ken was a straight man, Ban was a detective/teacher, Rock was a flexible, chaotic individual that can play as a good or evil protagonist depending on the story, etc.
Sometimes he can even play on this, having characters play roles outside of their niche to subvert the audiences expectations.
It's not something exclusive to him (Black Lagoon is also a series I can think of where they're actually actors playing a movie), but his is the most extensive.