John T Draper, a k a Cap'n Crunch is perhaps the most legendary phone phreak. The golden era of phone phreaking was in the late 60's and early 70's, and consisted of groups of phone addicts in New York, Florida, SF and elsewhere exploring and exploiting the phone system. He was one of the first to actually design and build a properly working blue box, with which you then make phone calls for free from any phone. Together with other phreakers in the SF Bay Area, he lead much of the phreaker exploration of the Ma Bell phone system just by trial and error. They actually did a lot of work for the phone company by reporting broken lines they came upon. They also got arrested and sent to jail one by one. 

In 1971 he became a  friend of Woz's, who naturally was very interested in phreaking and also tried to build his own blue box, which he eventually did. Cap'n Crunch actually wrote the first word processor for the Apple II computer, "EasyWriter". He was also one of the members of The Home Brew Computer Club, where Woz would make his legendary presentation of the Apple, in front of Steve Jobs and others.

The Cap'n Crunch cereal box whistle actually needed to have its third hole glued up, in order to produce the desired 2600 Hz tone. Cap'n Crunch spent some time in jail in 1972, in Lompoc minimal security prison for telephone fraud


Source: webcrunchers.com/crunch, discovery.com et al.