(Baptised name: Maria Isabella Puzorelli) She is the daughter of Alberto Puzorelli and the woman only known as Gabrielle. Her mother was a waitress at Goathead, Colorado cafe "Graham's Goodtime Grill". She was involved with an Italian man named Alberto Puzorelli, with strong connections to the New York mob under mobster Antoine Puzorelli (his father, her grandfather). Not much was known about their relationship, only that he dumped Gabrielle before he died under circumstances unknown, leaving her unknowingly pregnant with Shadow. Gabrielle would soon meet Casey Jones at her cafe. As Casey one day on one of his strolls accidentally killed a young purse snatcher, he set out on a self-discovery trip. During his journey, he came to Goat Head, Colorado, and met in "Graham's Good Time Grill" the waitress Gabrielle, who took him in the caravan after Casey was robbed. It can be assumed they either had a one-night stand or Gabrielle let him stay at her trailer, in the course of which he discovered her pregnant from her previous relationship, she had just finished prior to her encounter with Casey. Though she expected him to leave her, Casey surprisingly stayed. Overtime, their relationship blossomed into love and soon they were married. But this joy was short lived, Gabrielle gave birth to a daughter a few months later and Gabrielle or Gabby (so called by Casey) died giving birth, Casey called the girl Shadow. (TMNT Vol 1, #58).
With no other family, Casey became Shadow’s legal guardian. Before returning to his mother in New York, Casey scattered Gabby's ashes over a cliff. After reuniting his mother, he saw April O’Neil (who would quickly become Shadow’s surrogate mother). Shadow grew happily in a large family, which included not only Casey and April, but the Turtles (her "uncles") and their mentor Splinter (her "Grandpa"). Developing a particularly close relationship with Michelangelo and Raphael, who were living with them in the apartment complex at that time, Shadow became fond of video games (TMNT Vol. 2, #13). She once told April she wanted a baby brother.
After an episode in which she and her family, among others, dealt with Lilith and werewolves ("Darkness Weaves"), April and Casey sent her to Northampton, where she lived under the care of Splinter and Stainless Steel Steve.
As a grown up teenager, Shadow started a relationship with a boy from the area, Jay. Since she kept certain details of her life from him, Jay followed her one day secretly back to the Jones Farm, where he was caught by Metal Head and learned of the existence of Splinter and the Turtles ( TMNT Vol.4 # 6-7). Later, however, Shadow had learned to her horror that Jay had joined the corps of a radical xenophobic group called Xihad that was rigorously and ruthlessly against extraterrestrial influence on earth, introduced by the Utroms ( TMNT Vol.4 # 24).
In a post-apocalyptic, possibly alternative future Shadow studied martial arts as an adult, was a fully trained ninja warrior, and when looking for her missing sensei, successfully took down the Foot Elite (Tales of TMNT # 69)
Soon, however, Shadow encountered ghosts from her past: Her biological father was Albert Puzorelli, a mafioso who had died shortly after he had left her mother. His father, Antoine Puzorelli, learned of Shadows existence and hired the Foot Clan to abduct her for him.
One night when being baby-sat by Michaelangelo, Shadow heard a knock on the door and answered it. Captured by the Foot Clan, she was taken to her paternal grandfather, Antoine Puzorelli. When Raphael learned of Shadow’s abduction he sough council with the Foot, confirming their involvement. He then agreed to kill Antoine Puzorelli for them in exchange for Shadow, a mission he couldn’t complete. Michaelangelo stepped in, disguising himself as a priest in the cathedral where Shadow was to be baptised by Antoine under his family name, . Only moments after being baptised (making Antoine her godfather), Michaelangelo dropped his disguise and rescued her, taking her to the top of the cathedral and using his shell to make himself appear as part of the gargoyles statues. Shadow was then returned to Casey and April (TMNT Vol. 3, #6 - 8).
Antoine Puzorelli then had his thugs put his apartment on surveillance in an attempt to locate Shadow. When April caught on to this and told Casey, Casey, April, and Shadow went into hiding in the Turtles’ current hideout in the mausoleum of Westwood Cemetery. While Shadow watched, Casey accidentally clubbed Raphael when he returned to the hideout, thinking him an intruder. Shadow, Casey, and April met back up with Leonardo and Michaelangelo when they brought Donatello to their mausoleum hideout, where he was then revived (TMNT Vol. 3, #11, 12 & 15). When Leonardo chooses to give up his artificial, removable hand, Shadow asks if she can keep it. Leonardo gives her permission (TMNT Vol. 3, #23).
As she grew older, Shadow were taught the basics of self-defense, in which she proved to be a very gifted student. For various reasons, the Turtles have, however, up to now decided not to teach her all the secrets of Ninjutsu. Often Shadow does well in heavy fighting because of own talents and intelligence as well as the help from her "uncles"