Martin Hellman is an American cryptographer and professor known for his significant contributions to the field of cryptography. He is best recognized for co-inventing the Diffie-Hellman key exchange, a method that allows two parties to securely share cryptographic keys over a public channel. This innovation laid the groundwork for modern secure communications. In addition to his work in cryptography, Hellman has been an advocate for the ethical implications of technology and its impact on society. He has expressed concerns about the potential misuse of cryptographic tools and the importance of balancing security with privacy rights in the digital age.