Mike Mills

Michael Edward Mills (born December 17, 1958) is an American multi-instrumentalist, singer, and composer who was a founding member of the alternative rock band R.E.M. Though known primarily as the bass guitarist and backing vocalist of R.E.M., his musical repertoire also includes keyboards and occasional lead vocals. He contributed to a majority of the band's musical compositions and is the only member to have had formal musical training.

Description above from the Wikipedia article Mike Mills, licensed under CC-BY-SA, full list of contributors on Wikipedia.