Jazz Fenton is the older sister of Danny Fenton Viewing herself as the most rational and normal member of the family, Jazz often plays a surrogate parental role to Danny, thinking he is a naive child in need of guidance, unaware that she is often smothering him. 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.