John Draper aka Captain Crunch

From Wikipedia:

John T. Draper (born 1944), also known as Captain Crunch, Crunch or Crunchman (after Cap'n Crunch, the mascot of a breakfast cereal), is a former phone phreak.

Draper was the son of a U.S. Air Force engineer; he described his father as distant in an interview published on the front page of the Jan 13-14, 2007, issue of The Wall Street Journal. Mr. Draper himself entered the Air Force in 1964, and while stationed in Alaska helped his fellow servicemen make free phone calls home by devising access to a local telephone switchboard. He was honorably discharged from the Air Force in 1968, and did military-related work for several employers in the San Francisco Bay Area. He adopted the counterculture of the times and operated a pirate radio station out of a Volkswagen van.

A blind friend of John Draper's named Joe Engressia (now known as Joybubbles) informed him that a toy whistle that was, at the time, packaged in boxes of Cap'n Crunch cereal could be easily modified to emit a tone at precisely 2600 hertz—the same frequency that was used by AT&T long lines to indicate that a trunk line was ready and available to route a new call.[1] This would effectively disconnect one end of the trunk, allowing the still connected side to enter an operator mode. Experimenting with this whistle inspired Draper to build blue boxes: electronic devices capable of reproducing other tones used by the phone company.

“I don't do that. I don't do that anymore at all. And if I do it, I do it for one reason and one reason only. I'm learning about a system. The phone company is a System. A computer is a System, do you understand? If I do what I do, it is only to explore a system. Computers, systems, that's my bag. The phone company is nothing but a computer.” — From Secrets of the Little Blue Box by Ron Rosenbaum, Esquire Magazine (October 1971)

The class of vulnerabilities Draper and others discovered was limited to call routing switches that employed in-band signaling, whereas newer equipment relies almost exclusively on out-of-band signaling, the use of separate circuits to transmit voice and signals. Though they could no longer serve practical use, the Cap'n Crunch whistles did become valued collector's items. Some hackers sometimes go by the handle “Captain Crunch” even today; as a result of this incident 2600 The Hacker Quarterly is named after this whistle frequency. The expense of sustaining the unbilled phone calls, the redesign of the line protocols and the accelerated equipment replacement due to the blue box is difficult to calculate, or even to separate from something as complex and dynamic as the telephone long-distance network, but it is generally acknowledged to be a huge sum.

The 1971 Esquire Magazine article which told the world about phone phreaking got Draper in hot water. Draper was arrested on toll fraud charges in 1972 and sentenced to five years' probation. The article also brought him to the attention of Steve Wozniak. In the mid 1970s he taught his phone phreaking skills to Steve Jobs and Steve Wozniak, who later founded Apple Computer.[1] He was briefly employed at Apple, and created a telephone interface board for the Apple II personal computer.[1] Wozniak has said that the reason that the board was never marketed was that he was the only one in the company who liked him[2] and partially due to Draper's arrest and conviction for wire fraud in 1977. Draper wrote EasyWriter, the first word processor for the Apple II, in 1979. According to the Wall Street Journal, he hand-wrote the code while serving nights in the Alameda County Jail, then entered the code later into a computer. However, another account had him writing the code as he served his four-month sentence at the Federal Correctional Institution, Lompoc, California.
(Wikipedia - John Draper)