Dr. Calvin Zabo is man who becomes the villain Mister Hyde. Inspired by the classic tale of Jekyll and Hyde, he created a potion that allows him to relase his most base urges in a superhuman form.
He has encountered the Ghost Rider on the following occasions:
- Due to a head injury given to him by the Hulk, he was having problems transforming into Mr. Hyde. He harasses a waitress (Gina) and is tossed out by Fraser. Dr. Zabo then hits Fraser over the head with a glass bottle and runs. After a time he manages to turn into Mr. Hyde and winds up battling Ghost Rider. The penance stare has an unusual effect on him, as it causes Hyde to start transforming back into Zabo. However, Hyde flees before the transformation is completed. 
- ↑ Ghost Rider (1990) 4