Theodore “Ted” Kaczynski, who was dubbed the “Unabomber” by the FBI, was found dead in his cell at a federal prison medical center in North Carolina early Saturday morning at the age of 81.

A spokesperson for the federal prison system told The Associated Press that his cause of death hadn’t been determined yet.

Known "the Unabomber," he admittedly committed 16 bombings from 1978 and 1995 at airlines, universities, and computer stores, according to the Associated Press (UNABOM was an acronym for University and Airline Bomber). The bombings caused the deaths of three people and the permanent injuries of more than 20 others.

Kaczynski's story as a reclusive bomber who lived in a shack in the woods after becoming disillusioned with society and academia is relatively well-known — but he also had some Bay Area ties. He retreated to the one-room, hand-built shack in rural Montana with no running water following a stint as a teacher at UC Berkeley.

Originally, he was born in Chicago and was reportedly a child prodigy and went to Harvard at the age of 16. There, he participated in a volunteer psychological study in which he was subject to hours of extreme verbal and emotional abuse as a measure of how people could handle stress, according to Reuters.

He eventually earned a mathematics PH.D. from the University of Michigan. After that, according to the Berkeley Historical Plaque Project, he became the youngest professor ever hired at UC Berkeley at the age of 25. However, he was apparently wildly unpopular among undergraduates, who said he seemed nervous while teaching and was unresponsive during office hours. He resigned after two years, and in 1971 moved to a small plot of land in Montana.

There, he made and mailed deadly homemade bombs across the country — leading to major changes in how Americans mailed packages and boarded airplanes, as the Associated Press reported. He also sent a 35,000-word anti-technology manifesto called, “Industrial Society and Its Future,” to national newspapers in 1995 — which ended up leading to a tip from his brother.

FBI agents soon after found him in his Montana shack, which was filled with rambling journals, a coded diary, and explosives and bomb-making materials, ending what has been called "the longest and costliest manhunt" in American history.

The FBI described Kaczynski as "a twisted genius who aspires to be the perfect, anonymous killer," according to Reuters. But he refused to plead not guilty by way of an insanity, and eventually pleaded guilty instead. He was sentenced to four life terms plus 30 years in federal prison starting in 1998, where a psychiatrist diagnosed him as a paranoid schizophrenic. He was held in a federal Supermax prison in Florence, Colorado, since May 1998, until his transfer to the prison medical facility in North Carolina.

Feature image of  mathematician Ted Kaczynski, later a domestic terrorist known as the Unabomber, at the University of California, Berkeley, June 1968. Photo by Sygma/Sygma via Getty Images.