John "Jack" Pappas is the son of Mr. Pappas and Didi Stone. He is one of the main characters and was the team captain and quarterback for Grant High School's football team. He is portrayed by Greg Finley.
Jack and Adrian Lee had oral sex, so Grace broke up with him. His former girlfriend is Grace Bowman, then towards the end of season 1, he turns himself in for making fake IDs to help cover his friend. He is assigned to do mentoring to a 14 year old named Duncan and finds he has an interest in his 20 year old sister, Shawna.
In Season 2, Jack and Grace then rekindled their relationship. At the very beginning of the season, she had sex with him as an attempt to "keep him", but when her father died the same night, she pushed him away. Grace eventually accepted her father's death and got back together with Jack.
Over the summer, since she would no longer have sex with him, Jack cheated on her again with Madison Cooperstein. This led to the end of their relationship.
Jack is now seeing Madison (although he states that if Grace would take him back, he'd break up with her instantly).
He kisses Grace in And Circumstance at the end of the senior party (causing a break-up between Grace and Daniel). Jack has since broken up with Madison, and tries to convince Grace to be more then friends, which she doesn't really want. Later in the season Jack reveals that he is still in love with Grace, but doesn't want to live without sex to get back together with her. He dates Raven for a while and sleeps with her.
It was revealed in the episode Girlfriends by Amy Juergens that Jack and Grace Bowman have gotten back together. They will apparently go over to Amy and Ricky's apartment for dinner. There it is revealed that he had sex with Clementine. In the episode Property Not For Sale, the hooker Ginger enters his dorm room to offer herself and Jack ends up helping her to get back with her real family and escape her pimp.
In the episode Regrets, Jack gets beaten up badly by Pimp for giving money to his hooker in order to escape from him. He is in critical condition, has surgery and is in coma for months. In the episode Hedy's Happy Holiday House Jack wakes up from coma.