Diogenes Dagrepont Bernoulli Pendergast is the younger brother of Special Agent Aloysius Pendergast.
Diogenes was born in New Orleans, Louisiana, the second-born son of Linnaeus and Isabella Pendergast. A darkly curious child, Diogenes looked up to his older brother, Aloysius, but his elder sibling was often cold or intentionally cruel to him. By his own admission, Aloysius was a "terrible older brother."
As a young boy, Diogenes was raised in the Maison de la Rochenoire on Dauphine Street in New Orleans, often spending summers at the family estates known as Penumbra Plantation and Ravenscry. He attended St. Ignatius Loyola school on Lafayette Street in New Orleans, and at one point had his IQ tested at 210. He had no friends, as the other children were too afraid of him to go near him. Every bit as intelligent and capable as Aloysius, a childhood incident involving his brother left Diogenes color blind, heterochromic, and forever bent on vengeance. His sibling rivalry with Aloysius grew to full-blown hatred. He crucified Aloysius's beloved pet mouse, Incitatus, and began experimenting on animals, devising highly complex machines he called "pain factories" to lure, capture, and torture them. As he grew older, his family began to grow leery of his activities, and he abandoned active experimentation in favor of keeping a series of dark journals filled with what Aloysius described as "the most vile things ever put to paper." Aloysius burned the journals upon discovering them, further widening the rift between the brothers.
Tragedy again struck Diogenes at the age of eighteen, when an angry mob descended upon Rochenoire and burned the family mansion to the ground. Diogenes hid in the family crypt beneath the property, hearing the screams of his parents as they burned to death. When Aloysius returned two days later, the brothers had a private conference behind closed doors that left the elder Pendergast even more ashen than usual. Diogenes promptly walked out the front door and disappeared. His only contact with the family in the following years was to request various sums of money, which Aloysius at one point attempted to deny, prompting a rare personal missive from Diogenes that was chilling in its threatening allusions. He finally resurfaced on his twenty-first birthday to receive his inheritance, during which time he bragged to Aloysius of plotting a "terrible crime" before disappearing again. He was presumed dead in a car accident in the United Kingdom shortly thereafter.
The Diogenes TrilogyDiogenes resurfaced twenty years later, having faked his death to continue plotting his "terrible crime." He sent a simple cryptic letter to Aloysius in April containing only the date "January 28," followed by an identical mailing six months later while the FBI agent was investigating the murders of Jeremy Grove and Nigel Cutforth. When that investigation ultimately resulted in Aloysius being imprisoned and left to die, Diogenes - acting upon his need for a healthy Aloysius as a focus for his vengeance - staged a successful rescue, including providing for a discrete convalescence for his older brother, before disappearing once again.
With Aloysius recovered, Diogenes put his long-plotted plan for revenge into action, killing three close friends of his brother with very distinctive methods straight from the Pendergast family history books, and salting each crime scene with evidence pointing to Aloysius. Diogenes began taunting his brother by sending additional missives with clues to his next victims, although even the notes themselves were carefully orchestrated, appearing to forensic experts to have been written by Aloysius himself attempting to disguise his handwriting. Having apparently killed Margo Green and unable to locate Bill Smithback, Diogenes abducted Lady Viola Maskelene, daring his brother to come to her aid while pulling off an elaborate heist of the Museum of Natural History's prized diamond collection. Unbeknownst to Diogenes, however, the collection's finest specimen, the fabled Lucifer's Heart, was only a replica; the real one was safely locked away in the vault of the museum's insurance company. Faced with this revelation, Aloysius promptly stole the real Lucifer's Heart, luring Diogenes with the prospect of trading the precious diamond for Viola. Diogenes agreed, but after ensuring Viola's safety, Aloysius reneged, surrendering himself - and Lucifer's Heart - to authorities.