Zimmerman deserves his plaudits, though this one might be a bit misguided... It was actually Whitfield Diffie and Martin Hellman that came up with the concept of asymetric keys... Ron Rivest, Adi Shamir and Len Adleman (RSA) get credit for finding a mathematical algorithm that is suitable for this purpose. And Phil Zimmerman deserves credit for implementing the algorithm in code, and for the balls to release it openly in spite of the government and RSA breathing down his neck.

For further information I'd recommend Simon Singh's The Code Book.

-Blake