Julie-Su is the daughter of Luger and his second wife, Mari-Su. Almost as soon as she was born, Julie-Su's half-brother Kragok, and his twin-sister Lien-Da, despised her. She was virtually ignored by Luger as he carried out his duties as the Dark Legion. When Mari-Su died from an unexpected accident (whether Lien-Da and Kragok may have taken part in her death is still unknown), Julie-Su's memory was wiped by Kragok and Lien-Da. They had greater plans for the Dark Legion and had no desire for their detested sibling to share in them, so an elderly echidna couple, Simon and Floren-Ca, took care of Julie-Su and treated her as their own daughter. For most of her life, Julie-Su grew up in a loving environment, unaware of the truth that Simon and Floren-Ca were warned never to reveal. Yet she constantly wondered why something felt missing in her life. Holding back these feelings, she later became a support troop when she was thirteen.
Meeting Knuckles & Chaotix
When the Dark Legion and Knuckles eventually clashed, the results were a destroyed headquarters and complex and an angry Julie-Su, separated from her compatriots. Upon discovering Vector, she attacked him, drawing Knuckles, Mighty, Espio, and Charmy to her. Later on, she faced Knuckles alone, and was forced to work together with him after a brief battle, during which her identity as a girl surprised Knuckles. Because of her association with the Dark Legion, Julie-Su was mistrusted at first, but gradually won over Team Chaotix, Knuckles, and Locke's respect and friendship (except for Vector).
Julie-Su discovered the truth about her past and has developed a more romantic involvement with Knuckles, due to their unacknowledged recognition through a sixth sense the Echidnas refer to as the "Soultouch". Together with the other Chaotix, she has left Angel Island to live on the surface in Knothole Village, working freelance with the Freedom Fighters. This has led to her participation in battles against various enemies, including the Metal Sonic Troopers, Destructix, Mammoth Mogul, and Ixis Naugus. She later takes Amy Rose under her wing, teaching her skills that likely aided the pink Hedgehog in uncovering the relationship between Fiona Fox and Scourge the Hedgehog.
Mobius: 25 Years Later and Dark Mobius
Two alternate future versions of Julie-Su have been shown. In them, Julie-Su is partnered with - but not married to - Knuckles, because they both believe in commitment over ceremony and they have a daughter named Lara-Su. In one future, nicknamed "Dark Mobius", Julie-Su went into hiding while she was pregnant after coming to the realization that her husband was being driven mad by all of the chaos energy inside of him.
After Knuckles became the new Enerjak, slaughtered all of Mobius' greatest heroes and villains and conquered Mobius, Julie-Su and their daughter Lara-Su became part of an underground resistance that tried to undermine Enerjak's rule and find some way of defeating him. She was killed by Enerjak's "Prelates" during a raid but was later resurrected along with the rest of the fallen after Lara-Su usurped her Father's power using The Sword of Acorns and became the new Enerjak.
The other Julie-Su, from Mobius: 25 Years Later, was always there for her daughter, however, refused to let her become the next Guardian of Angel Island. The future Julie-Sus are both protective of Lara, and only want what's best for her. In Mobius: 25 Years Later, Julie-Su is concerned by her husband's unusual behavior. This version of Julie-Su lost her memory of the original M:25YL future after Lara-Su and Sonic's trip back in time altered history, as she had no method by which to escape losing her memory as the future altered. As such, the alternate Julie-Su is unaware of the rightful timeline.