one-man band

Short definition from Wiktionary

Noun

1. 1
   A musician who plays several musical instruments at once.
2. 2
   A musician who plays several musical instruments at once: A band in which the frontman does most of the work and is the spotlight or the center of attention, usually to the detriment of other band members.
3. 3
   An organisation or business that is effectively run by only one person.
4. 4
   Alternative form of one-man band.