Liberty Danielle "Libby" Folfax (voiced by Crystal Scales) is one of the main characters in The Adventures of Jimmy Neutron: Boy Genius. She is an African American first appearing in the Jimmy Neutron: Boy Genius film. She is Cindy's best friend and Sheen's love interest which seemed to have started in the second season. She is fifth grader and is eleven years old (twelve starting from "The Tomorrow Boys" and onwards)
She also has a little brother (name not mentioned) seen in the beginning of "Make Room for Daddy-O" as the legs in the saw the lady in half trick.
Not much is known about her family, but she is known to have a mother and father. In the episode "Beach Party Mummy", she discovers that she is related to Queen Hasabataslapia.
Libby's main interest is music with funky rhythm. When she experiences music withdrawal, she faints (as revealed in "Hall Monster"). She also loves electronic gadgets and being stylish. In the first season she does not appear in the title logo. When she becomes more involved in the show, however, she is added to the logo in the second season and is still on it in the third season. Unlike Jimmy's friends, Libby is shown to do well in school, but isn't at the level of Jimmy or Cindy in terms of intellect. According to "Nightmare in Retroville", she is a vegetarian.
Her favorite band is Graystar whom she has invited to Retroville twice (in "Attack of the Twonkies" and "The Tomorrow Boys"). She is also revealed to have piano playing skills (as revealed in "My Big Fat Spy Wedding" and "Vanishing Act").
Libby once in a while returns Sheen's interest in herself, but not when Sheen is not annoying her with his overbearing mentions of Ultra Lord and occasional flirting. Along with Cindy, Libby won a first place trophy for riverstomp dancing at the school contest in "Battle of the Band"; Jimmy, Carl and Sheen almost beat the girls with their electronic rock music guitars and drums, but at the last minute, Carl and Sheen destroyed their own instruments in a jealous quarrel, and the boys ended up with was an eighth place trophy after Carl did his giant snot bubble trick.
Libby has full knowledge about Jimmy and Cindy's relationship with each other, as Cindy does not want to express her feelings to Libby about it and stammers each time Libby mentions it. Although, Libby sometimes joins Cindy in teasing Jimmy. Libby once in a while returns Sheen's interest in herself, but not when Sheen is not annoying her with his overbearing mentions of Ultra Lord and occasional flirting.
In "The Tomorrow Boys", Libby had become the evil dictator of Retroville after Carl accidently got the Megalomanium to her birthday party out of confusion by the perfume and the Megalomanium. When she opened the present, she became mad with power, thus making her the evil dictator of Retroville.
In "The N-Men", Libby gains the super power of invisibility, based on how she was putting on vanishing cream for her acne when she and the group were exposed to the Van Patten Radiation Belt. Libby calls herself "Invisible Sister". She learned in the military station that she also had the ability to generate a force field, and create a pad to float herself in midair.
In The League of Villains, Jimmy, Carl, Sheen, Cindy and Libby's superpowered have been mixed up. Libby is the one who had ended up with Carl's superpower; Burp Boy. This made her gain the ability to make gigantic burps enough to make anyone go flying.
- Libby will meet Jeffrey and his team in Jeffrey & Friends meet Jimmy Neutron: Boy Genius.
- Libby will join the Cyberchase Fighters in Michael Buzz and Delete meet Jimmy Neutron Boy Genius.
- Libby is a huge fan of Austin Moon.