The Shi'ido individual known as Mammon Hoole, who later went by (Indeterminate) Hoole after choosing to drop his given name, hailed from Sh'shuun and was male. A distinguished geneticist and graduate of the prestigious Chandrilan Academy of Sciences, he, along with his Shi'ido colleague Borborygmus Gog, became a member of the Ministry of Science within the Galactic Republic. Initially, their work for the Republic involved devising defenses against the bioweapons employed by the opposing Confederacy of Independent Systems during the Clone Wars. Secretly, however, at the behest of Chancellor Palpatine, they began conducting experiments focused on manipulating the very essence of life. These clandestine experiments ultimately resulted in the creation of Trioculus, a mutant distinguished by having three eyed.
When Palpatine transformed the Republic into his Galactic Empire, Hoole and his associate aligned themselves with the new power structure. Emperor Palpatine, in his self-proclaimed role, provided them with a laboratory situated on Kiva, tasking the Shi'idos with pushing their experiments even further. Tragically, the immense power generators utilized in the lab led to the complete annihilation of all life on Kiva. In contrast to his colleague, Hoole experienced a moral crisis and made the decision to abandon his service to the Empire.
Despite his attempts to avert the catastrophe, Hoole was held solely responsible for the Kivan genocide, leading him to renounce his given name and seek a different path. After earning a degree in sentientology from the Galactic Research Academy located on Koaan, Hoole embarked on a journey across the galaxy as a traveling anthropologist, making stops on planets such as Tatooine and Arzid.
Following the Empire's destruction of Alderaan, Hoole took in the Alderaanian children Zak and Tash Arranda, to whom he was distantly related through marriage. Together, Hoole and the Arrandas embarked on various adventures, ultimately compelling the Shi'ido scientist to confront both his past actions and his former colleague.
Eventually, Palpatine's Empire was defeated, giving rise to the New Republic. During the height of this new government, Senior Anthropologist Mammon Hoole shared his research and observations with Ann Margaret Lewis, whose work resulted in the creation of The Essential Guide to Alien Species.
During the era when the Galactic Republic governed the galaxy, Mammon Hoole's birth occurred on Sh'shuun, a planet characterized by its dense jungles and situated within the Unknown Regions. He was a member of the Shi'ido, a species of humanoids known for their extended lifespans and remarkable ability to change shape at will. He had at least one sibling, Moloch, who later entered into marriage with Beryl, a Human woman originating from Alderaan. Given the Shi'ido belief that all relatives were considered immediate family, Hoole embraced his new Alderaanian kin as if they were his own.
Throughout his academic time on his homeworld, Hoole distinguished himself as a dedicated and exceptional student. Eventually, he departed from Sh'shuun to pursue a career in science. He enrolled in the Chandrilan Academy of Sciences, where he formed a friendship with Borborygmus Gog, another Shi'ido. United by their shared enthusiasm and ambition in research, they both successfully graduated. Following their time at the academy, the two changelings went their separate ways for a period. Gog dedicated his time to infiltrating secretive cloners residing on Khomm and Kamino, while Hoole chose to study with renowned geneticists on Ithor and Lur.
Hoole openly acknowledged his own brilliance and yearned for recognition in the field of genetics, as he had grown tired of simple cloning endeavors and sought to manipulate the very creation of life. It was this hubris that ultimately led him to a four-year period he would later come to regret.
In the fifth month of the year 22 BBY, the Republic and the Confederacy of Independent Systems, a separatist movement under the leadership of former Jedi Master Count Dooku of Serenno, engaged in a war that erupted. Due to the clone troopers grown on Kamino that made up the Grand Army of the Republic, the conflict became known as the Clone Wars. Around 20 BBY, the Confederacy began deploying clone-killing bioweapons. In response, Supreme Chancellor Palpatine, the Republic's leader, initiated a new research project that reunited Mammon Hoole with his former colleague, Borborygmus Gog.
Under the supervision of Sly Moore, Palpatine's Umbaran aide, the two Shi'ido were initially tasked with assisting the Republic's Ministry of Science in developing countermeasures against the Confederacy's attacks. However, their groundbreaking discoveries soon captured the personal attention of the Chancellor. At his request, Hoole and Gog devoted themselves to experiments in abiogenesis—the spontaneous creation of life—rather than mere replication. Moore provided the scientists with a subject for their experiments, a compliant Human female from Bordal named Niobi.
The challenge of creating life was so captivating and ambitious that Hoole and his colleague disregarded any moral or ethical considerations. However, their initial attempts went awry, resulting in the birth of multi-headed homunculi with deformed limbs. Eventually, Hoole and Gog managed to eliminate most abnormalities and produce a single viable specimen. However, the child remained a mutant with a third eye on his forehead, which led to him being named Trioculus. Almost immediately, the newborn child and his mother were whisked away under the orders of Sarcev Quest, one of Palpatine's protégés. In their arrogance, the Shi'ido scientists blamed their failure on Niobi and began using themselves as test subjects for further experiments. They even ventured to combine their Shi'ido genes with those of a Clawdite, another shape-shifting species from Zolan, which amplified their natural shape-changing abilities to an unprecedented extent.
Following the slaughter of the Confederacy leaders in 19 BBY, the Clone Wars came to an end, leaving deep scars across the galaxy. Palpatine, secretly a powerful Sith Lord known as Darth Sidious, dismantled the Republic from within and replaced it with his autocratic Galactic Empire. Hoole and Gog had completed what they deemed "basic" experiments and required a larger laboratory. The newly appointed Galactic Emperor offered them a vast, private laboratory on Kiva, where they could explore the mysteries of life and death more freely. At the time, Hoole, like most of the galactic community, was unaware of the Emperor's true evil and was too excited about the new opportunities to be concerned with political ethics, leading him to accept Palpatine's offer. In their laboratory, the geneticists realized they needed to harness immense power to create life from nothing. To achieve this, they constructed massive generators capable of concentrating the energy of an entire star into a small test tube. Unbeknownst to Hoole, this process would inevitably lead to the destruction of all life on Kiva. While Gog was responsible for ensuring the experiments remained within safe limits, he deceived Hoole and assured him they would cause no harm. However, the Shi'ido lost control of their experiments, and instead of creating life, they unleashed a surge of energy that wiped out every living organism on Kiva, leaving its inhabitants as disembodied wraiths. Hoole attempted to broadcast a warning, but the deadly energy wave disrupted the transmission before it could reach the Kivans. Only Hoole and Gog managed to escape the disaster.
The accident that claimed millions of Kivan lives triggered a profound moral awakening in Hoole. Although Gog was clearly responsible for the events on Kiva, Hoole's pride prevented him from blaming anyone but himself, as he believed he should have recognized his partner's deceit. Disgusted with his life and the Empire, he decided to leave the Emperor's service after four years of dangerous experiments. Gog, however, remained with the Empire and implemented Project Starscream, aimed at creating an army of supersoldiers. The Imperials placed the blame for the Kivan genocide on Hoole, deliberately destroying his reputation and protecting Gog. While the latter's responsibility for the massacre was erased from all records, the Empire spread the story that a Shi'ido named Mammon had exterminated an entire civilization. Haunted by the horrors of Kiva, Hoole was forced into exile. In an attempt to bury his past, he also chose to abandon his given name, which had become synonymous with a planet-killer condemned by everyone in the galaxy, including the Emperor.
Around 16 BBY, Hoole began a new chapter in his life by enrolling at the Galactic Research Academy on Koaan. Upon completing his studies, he became a professor of anthropology, dedicating himself to documenting the customs and traditions of various species throughout the Known Universe. Now holding the title of Senior Anthropologist, Hoole wandered the galaxy, utilizing his species' remarkable shape-shifting abilities to infiltrate numerous alien cultures. He notably visited the sun-scorched planet Tatooine, where he studied the societies of the Jawa and Ghorfa. During his time there, Hoole gained acceptance into the Nkik clan of Jawas by disguising himself as one of them, and he even temporarily resided in the palace of the local crime lord Jabba the Hutt. A detailed account of his time on Tatooine was published under the name "(Indeterminate) Hoole."
During his years as an anthropologist, Hoole typically worked alone or with his custom-made research assistant, DV-9. He only took on assistants when studying species he couldn't mimic. Tragically, some of these assistants were devoured by Arachnors on Arzid. One such assistant was Chlar Kotchmin.
In 0 BBY, Grand Moff Wilhuff Tarkin chose to demonstrate the destructive capabilities of the Death Star, a moon-sized battle station armed with a planet-destroying superlaser, on Alderaan, the homeworld of his sister-in-law Beryl and her relatives, Kalf and Milessa Arranda. Their two children, Tash and Zak Arranda, were on a field trip when the Death Star's superlaser struck Alderaan, leaving them orphaned. As their closest living relative, Hoole became their guardian. He kept the children on his starship, the Lightrunner, where he and DV-9 educated them while Hoole traveled to different parts of the galaxy for his studies. He continued his work until the trio angered key members of the Empire by interfering with Borborygmus Gog's Project Starscream, resulting in a bounty being placed on their heads. Unable to continue their research, the three settled into a home in an undisclosed location, possibly New Alderaan.
In his home-based laboratory, Hoole began compiling his collected notes and data into a book. As the threat of Imperial discovery lessened, Tash and Zak went off to college. Once the data was compiled, Hoole sent it to Ann Margaret Lewis, a professional writer, who completed the text and sent it to a publisher on Coruscant. Recognizing the book's importance, the publisher immediately published it, and The Essential Guide to Alien Species became available on most planets.
When interacting with his adopted niece and nephew, Hoole often assumed a Human-like form with a few distinct alien features, such as extra-long fingers and dark gray skin. He was generally able to conceal his emotions, maintaining a stern and unreadable expression. When angered, his gaze became sharp and cold.
Even among the Shi'ido, Mammon Hoole was an exceptionally skilled shapeshifter. Legends even tell of him once assuming the form of a Whaladon.
Mammon Hoole was first referenced in the 1995 reference book The Illustrated Star Wars Universe, where he was presented as the in-universe author of the Tatooine chapter. In that book, he was formally referred to as "(Indeterminate) Hoole." His character was further developed in Star Wars: Galaxy of Fear, a series of young adult horror novels by John Whitman that featured the Shi'ido scientist and his young wards. In 2001 and 2006, Hoole was once again used as the in-universe narrator in both editions of The Essential Guide to Alien Species. In 2009, Adrick Tolliver revisited Hoole and his wards in Death in the Slave Pits of Lorrd, a short story that appeared on StarWars.com. The story took the form of an essay written by Tash Arranda and edited by DV-9, accompanied by hand-made drawings by Pablo Hidalgo.
In Army of Terror, the sixth book in the series, Hoole revealed that he had begun working for the Empire "almost twenty years ago" from the current time. According to The Essential Reader's Companion, the Galaxy of Fear series took place between 6 and 18 months after the Battle of Yavin, which occurred in 0 BBY. This placed the beginning of Hoole's work with the Empire around 20 BBY. However, the 2005 movie Star Wars: Episode III Revenge of the Sith showed that the Empire was not founded until 19 BBY, one year later. In Aliens in the Empire, an online supplement to the 96th and 97th issues of Star Wars Insider magazine, Abel G. Peña retconned Hoole's early activities as taking place during Palpatine's last term as Chancellor of the Republic.
Mammon is a biblical term for the pursuit of wealth, often personified as a deity. In Paradise Lost, John Milton, the 17th-century English poet, featured Mammon as one of the fallen angels in hell, alongside Belial and Moloch. These demonic names have been used in the EU as Shi'ido names.