I'm your hall monitor, Danny. And there's no place you can go that I can't follow. Except there."

*Jasmine "Jazz" Fenton is the older sister of Danny Fenton, the titular character of Danny Phantom, and later, his clone Danielle. Viewing herself as the most rational and normal member of the family, Jazz often plays a surrogate parental role to Danny, thinking he’s a naïve child in need of guidance, unaware that she is often smothering him. Once she learns Danny's secret, Jazz not only doesn't say anything until he's ready as well as help keep his secret but begins to realize her brother is growing up. Once Danny accepts that Jazz knows, they become much closer.

Like her brother, Jazz is a young teenage with a similar facial structure and slender figure like her mother. She inherited her father's aqua blue eyes and her mother's auburn hair (but with an orange tint), which reaches down to her hips. She also wears dark pink lipstick.

Jazz wears an aqua headband, a black long-sleeve v-neck shirt, aqua pants, and a pair of simple, black flats. Other than wearing a black tank top in "Fenton Ghost Peeler" and two different Ember costumes, Jazz is one of the characters who has the fewest costume changes.

At school, Jazz is apparently popular and very social. She gave a school spirit speech that was applauded and cheered on by everyone in attendance.

While she may not consciously know it, Jazz tends to think that her intelligence makes her superior to others and can go completely bonkers if she is shown to be wrong. She tries to use her knowledge and her understanding of psychology to point her parents in a more "normal" direction, even if it sometimes is quite annoying to others.

Insisting that she is the most rational member of her family, Jazz often criticized her parents' obsession with ghosts. She started off as a rather snobbish genius who refuses to be associated with her parents.

Jazz gradually develops as the show progresses, embracing the family ghost-hunting, and enjoying the activity. Her sudden increased interest in ghosts causes her to believe that she is suffering from "ghost envy", stating she desires to be a ghost if only to get her parents' attention.

Being the oldest sibling, Jazz takes it upon herself to be the "mature" adult. She believes she is an adult stuck in a teenager's body and wants to be a good role model for her younger brother. Her belief in herself being an adult made her vulnerable to Youngblood, a ghost-pirate kid whose powers are designed to either evade or subdue adults.

However, Jazz finally embraces her childhood through her "one weakness": Bearbert Einstein, her favorite stuffed teddy bear. When Danny tore the little bear apart, she threw a fit, jumping up and down while crying. This makes her realize that she doesn't have to be the adult all the time and that there's nothing wrong with being a kid sometimes, ultimately creating a balance between the two.

Jazz is often overprotective of her little brother and is constantly concerned about his development and well-being, much to Danny's annoyance.

She often bossed Danny around and acts more like a mother than a sister, but ultimately, she meant well. Jazz eventually develops a deep respect for her brother's selflessly heroic nature and supports him through "thick and thin".*