Before he played a massive part in laying the foundation for the Marvel Cinematic Universe in 2008 with "Iron Man," Jon Favreau was landing plenty of acting roles in the 1990s. One of his notable appearances was in the "Seinfeld" episode "The Fire" as Eric the Clown, a small yet humorous character that George fought with for not knowing who Bozo was.
The MCU’s favorite android, Ultron, guest-starred in the hilarious Season 9 episode "The Apology," where he played Jason Hanky, an alcoholic who is going through a 12-step program but refuses to apologize to George. At the time of his appearance, Spader was coming off of feature films like "Stargate" and "Critical Care."
Patton Oswalt was briefly seen as Pip the Troll in “Eternals,” during a post-credits scene with Harry Styles' Eros/Starfox. However, one of his first official acting jobs was in the "Seinfeld" Season 6 episode "The Couch," where he played the clerk at a video store where George tries to rent "Breakfast at Tiffany's."