MXR, also known as MXR Innovations, was a manufacturer of guitar effects units, co-founded in 1973 by Keith Barr (who went on to found Alesis) and Terry Sherwood (who went on to co-found Applied Research & Technology). MXR was based in the United States in Rochester, New York. MXR Innovations, Inc. was incorporated in 1974. The MXR trademark is now owned by Jim Dunlop, which continues to produce the original effects units along with new additions to the line.

Read more about MXR:  History, Jim Dunlop and MXR