|Appeared in||The Real Ghostbusters;|
|Played by||Peter Cullen|
Cyrus Spengler runs Spengler Laboratories. He wants his nephew Egon to help him. He arrives in New York to see how his nephew is doing and reveals that he doesn't believe in ghosts, much like Winston's father Edward Zeddemore.
Cyrus essentially forces Egon to make good on a promise long ago to help him in his studies. He has Egon work at his lab feeding rats. When Cyrus lets the other Ghostbusters have Egon back for at least one more bust, he accidentally frees the Stay Puft Marshmallow Man from the Containment Unit. Only then does he realize that ghosts are indeed real and that the Ghostbusters need Egon. After Stay Puft was recaptured, Cyrus absolves Egon of his obligation and tells his nephew Egon that he should stay with the Ghostbusters.
Cyrus has been shown to be a no-nonsense pragmatist and initially doesn't believe parapsychology to be a legitimate science. He does prove to be a decent guy upon learning that the paranormal is very real and shows support for Egon pursuing it. He also has extreme astigmatism, mistaking Slimer for a cat upon losing his glasses and missing seeing a real ghostbusting emergency.
- Cyrus gives us one of the two sole clues regarding Egon's father in both animated series: That he has a brother. Plus Cyrus illustrates the notion that scholars and scientists run in the family. The other clue is Egon mentioning that his parents didn't speak to him for a week following his sole A-Minus grade in college.  Implying his father was a harsh perfectionist.
- In Ghostbusters Issue #2 page 19, Cyrus watches Jacquelyn and Zac take a photograph by the bear statue.