Phil Zimmerman is an American (born, 1954) computer scientist and Web developer: his fame is due to his writing of the original email encryption program: Pretty Good Privacy. The first version of Pretty Good Privacy was written in 1991; it has since been developed and expanded upon by a number of prominent scientific communities: such as MIT. Pretty Good Privacy is viewed as a "standard" within the email encryption industry, and has therefore helped secure millions of sensitive email messages.
Zimmerman did run into legal issues with the US Government due to the strength of Pretty Good Privacy. Due to the strength of it's encryption, the US Government saw the program as a security risk, and during the mid 1990's contemplated filing charges against Zimmerman via it's US Export Regulations. Eventually, any legal issues disappeared, and Zimmerman was able to continue developing Pretty Good Privacy through his new company PGP Incorporated.
Present day, Pretty Good Privacy has a number of versions: some which are free and are open source, others which are commercial. The open source nature of some Pretty Good Privacy, allows it's users to check the program for security flaws and backdoors. PGP Corporation is the owner of the code base of Pretty Good Privacy, and as of 2013, is owned by Symantec Corporation. PGP International is another entity, based in Europe, which has released an open source version of PGP.