Electro-Harmonix is a New York-based company that makes high-end electronic audio processors and sells rebranded vacuum tubes. The company was founded by Mike Matthews in 1968. It is best known for a series of popular guitar effects pedals introduced in the 1970s and 1990s. Unknown to most people, EH also made a line of guitars in the 70's.
During the mid-1970s Electro-Harmonix established itself as a pioneer and leading manufacturer of guitar effects pedals. Electro-Harmonix was the first company to introduce, manufacture, and market affordable state-of-the art "stomp-boxes" for guitarist and bassists, such as the first stomp-box flanger (Electric Mistress), the first analog echo/delay unit with no moving parts (Memory Man), the first guitar synthesizer in pedal form (Micro Synthesizer), and the first tube-amp distortion simulator (Hot Tubes). In 1980, Electro-Harmonix also designed and marketed one of the first digital delay/looper pedals (16-Second Digital Delay) and a line of guitars in the 70's.
source: Wikipedia