John Draper —

Dubbed “Captain Crunch” for finding that a toy whistle shipped in boxes of Captain Crunch cereal had the same frequency as the trunking signal of AT&T, 2,600Hz. This discovery was made with the help of Joe Engressia. Although Joe was blind, he could whistle into a phone and produce a perfect 2,600Hz frequency. This tone was useful for placing free long distance phone calls.
Reminds me of the movie "The Core" when the hacker gets a gums tin wrapper and uses it to give free long distance calls to the scientist.