It wouldn't be Guardians Of The Galaxy without a Rob Zombie cameo. While it paid off in a major way, Guardians Of The Galaxy was once seen as a big gamble on Marvel's part. Opening up the cosmic side of the MCU had a lot of opportunities to backfire, especially considering the comic was one of Marvel's more obscure from a mainstream audience perspective. Thankfully director James Gunn - who had previously helmed darker projects like Super - brought a great deal of heart and humor to the project, in addition to a top-notch cast, including Zoe Saldana (Avatar) and Dave Bautista, and it made Chris Pratt a star.
The cast and Gunn returned for Guardians Of The Galaxy Vol. 2, which revolved around Peter - AKA Star-Lord - being reunited with his father Ego (Kurt Russell), who just happened to be a planet. The team also played a major role in Avengers: Infinity War, where they rescue Thor and become involved in the fight to stop Thanos. This leads to some dark consequences for the Guardians, with the aftermath playing into the events of Avengers: Endgame.
James Gunn loves to load his Guardians Of The Galaxy movies with easter eggs, such as the icky space slugs from his first directorial effort Slither appearing in the Collector's (Benicio del Toro) room in the first movie. Gunn is good friends with rocker and director Rob Zombie, best known for his Halloween remake and The Devil's Rejects. Zombie made a vocal cameo in Slither as a doctor and returned once again as the voice of God in Super.
James Gunn has explained that a Rob Zombie cameo has become something of a signature, which is why he made another vocal cameo in Guardians Of The Galaxy. Zombie voiced the "Ravager Navigator," who can be heard in the Milano in the first act. Zombie returned again for Guardians Of The Galaxy Vol. 2, where he played the key role of "Unseen Ravager." The odds are good Zombie will return in a vocal capacity once more for Gunn's upcoming The Suicide Squad and Guardians Of The Galaxy Vol. 3.
Rob Zombie is unlikely to physically appear in a future Guardians Of The Galaxy movie, however. Outside of some random voice over work, such as playing The Lizard in 2003's Spider-Man: The New Animated Series, he almost never appears on camera as an actor. That could always change of course, but for now, Zombie seems more comfortable behind a camera when it comes to filmmaking.