Harold Locke Hazen (August 1, 1901 – February 21, 1980) was an American electrical engineer. He contributed to the theory of servomechanisms and feedback control systems. In 1924 under the lead of Vannevar Bush, Hazen and his fellow undergraduate Hugh H. Spencer built a prototype AC network analyzer, a special-purpose analog computer for solving problems in interconnected AC power systems. Hazen also worked with Bush over twenty years on such projects as the mechanical differential analyzer. This early work, and the binary algebra used, would be foundational to the emergence of electromechanical and digital computers in later decades.