The Caretaker playing the banjo
The banjo was a four- or five-stringed instrument from the planet Earth.
In 2371, the Caretaker appeared to the crew of the USS Voyager as an old man playing a banjo. (VOY: "Caretaker") Because of this, some members of Voyager's crew came to refer to him as "Banjo Man". (VOY: "Projections")
The call sheets for "Caretaker" featuring the banjo have notes that this banjo was muted. A sideline musician provided the professional music.
Banjos were also mentioned in the song "I've Been Working on the Railroad". (VOY: "Virtuoso")