Peter MacDougall is Amy's very geeky older brother and the son of Hank and Pat MacDougall. In early episodes, he revealed his dislike of his current brother-in-law, Robert Barone, and his behavior often repelled the rest of the Barones, despite his conflict with Robert, it was noted that the two have more in common than they think with the most common aspect being that the two were overshadowed by their younger sibling and got along better after realizing this (this revealed Amy to be the favorite child of the MacDougall family). He owns a comic book store that now belongs in Robert's old apartment on Long Island. He owns a cat named Miss Puss and a pet snake, and he is in a relationship with Peggy after finding out she was a nerd too.
- Before Chris Elliott was chosen to play the part of Peter, actor and writer Paul Reubens, who is best known for his role as Pee-wee Herman, debuted the character originally named Russell in the episode "Hackidu". In the same episode, he mentioned that he kept only a pet snake. Also, the comic book store was located in New Jersey before the writers decided to locate the store and, for that matter, the entire MacDougall family to Pennsylvania.
- Although the character was revised, Peter sort of became Russell as Peter mentioned that he saw Raymond in the comic book store in episode Just a Formality (which was Russell after Paul was arrested).
- Paul Reubens was replaced because he was arrested for child pornography after the episode "Hackidu" aired and could not reprise his role as Russell in later episodes as he was serving jail time, Chris Elliot took over the role and the character was renamed Peter.
- In addition to selling DC comic books, Peter created his own comics, Zombie Blood Chronicles, which never gained much support from his Presbyterian family.
- PETER: (to Robert, with disdain) Hello again. (joyously) Ray! How wonderful to see you!
- PETER: (to Ray, who has refused to buy some comic books for Ally) Don't you get it, you Long-Island, suburban automaton? You can't hear the
truth over your lawnmower, man!
- PAT: It's just that...over the years, there have been so many times when Amy was very unhappy.
- PETER: (scoffs) You don't know the half of it, Mama. So often she would come into the store and curl up in the used comics section and cry like Little Lotta!
- PETER: (to Ray) You know...even though your brother and I have our differences, you and me are totally copacetic, Home Fry!
- PAT: I'm sorry, Peter, but we gave your room to Jesus!
- PETER: (screaming) Jesus doesn't need a room! His dad didn't throw him out! I need my kitty! (Calling out) Miss Puss! Miss Puss-Puss!
- HANK: She's outside.
- PETER: (aghast) What!? Outside?! NO! Miss Puss is an inside cat!
- PAT: ...Not anymore.