Ruby Dinsmore is a new girl at P.S. 38, and has a crush on Nate. Randy Betancourt has a crush on her, but she doesn't feel the same about him.
"I'm glad that you're staying put!"
―Ruby's last words
Upon moving into P.S. 38, Ruby Dinsmore was constantly chased down by two students, Nate Wright and Randy Betancourt, who both had a crush on her. She gave Nate a can of root beer when Artur Pashkov told her Nate was hungry, but when Randy shook it (something only witnessed by Drama ClubPresident Dee Dee Holloway), the soda sprayed into Nate's face. Martin Wright eventually told Nate that they are not moving to California, which made an excited Ruby kiss Nate, breaking Randy. After some time, Randy waved her off, deciding that he could live without her.
She appeared in Big Nate: Blasts Off, which was her first and only appearance. She only appears in the novels, she has never appeared in the comic strip, not even once.