What is the name of Jesse Katsopolis's father?

Jesse Katsopolis's father is Nick Katsopolis.

Nick, played by John Aprea, is introduced as Jesse and Pam Katsopolis's father and as the maternal grandfather of D.J., Stephanie, and Michelle Tanner. He owns an insect-extermination business, where Jesse works early in the series before pursuing other careers.

The Katsopolis family is strongly associated with Elvis Presley fandom, enthusiasm for hair, and a lively Greek American family dynamic. Nick is strict with Jesse but also deeply protective; when Jesse considers leaving the extermination business, Nick takes it as a personal family betrayal because he built the company himself.

A common mix-up is confusing Nick with Danny Tanner, whose daughters Jesse helps raise. Jesse later names one of his twin sons Nicholas—Nicky—in honor of his father, making Nick's family connection especially visible in the show's later story.