Mount Sims (also Mt. Sims) is the stage name of Matthew Sims, a Berlin-based American DJ, performance artist, producer, and former lead singer and bassist of the Milwaukee-based band Citizen King. Starting Mount Sims as a purely electronic music act, later releases have also shown influences from post punk, new wave, and darkwave. Sims is almost exclusively responsible for every aspect of his music, providing vocals, instrumentation, and production. He was originally supported by two dancers, whereas the last incarnation under the altered spelling Mt. Sims was a three-piece band that included Rand Twigg on bass and Andre Lange on drums.

His first album, "Ultra Sex" (2002/International DeeJay Gigolo Records (Europe) and Emperor Norton Records (USA)), was released to good reviews. It was influenced by German and British New Wave bands, funk, and electronica. It was a concept album that focused on the themes of technology and sexuality. The album contains the tracks "How We Do" and "Rational Behaviour."