Ted Kaczynski was convicted of several bombings between 1978 and 1995. Three people were killed and about 20 injured in the Unabomber's 16 different bombings.
In a manifesto published by The Washington Post and The New York Times, Ted Kaczynski denounced technology and modern development. He was also critical of industrial society.
Wrote a manifesto
The hunt for Kaczynski was one of the largest in the history of the American police and it was the published manifesto that ultimately became his downfall. His brother recognized wording in the manifesto and tipped off the police.
The former mathematician and university lecturer was sentenced in 1996 to life imprisonment without parole.
He was found in his jail cell on Saturday morning, a prison spokesperson said. The cause of death is yet to be determined.
Ted Kaczynski was 81.