In all my years as a musician outside of Puerto Rico, I always get asked the following question everywhere I go: "What instrument is that?" To which I always reply: "It's a cuatro".
The Puerto Rican cuatro is a very peculiar instrument in the sense that its name is in Spanish, but it does not really describe the modern version of the instrument.
The cuatro as an instrument has five double strings, ten strings total, but cuatro in Spanish means four, so why the reference to the number four?
The origins of the instrument can be traced back to the end of the 18th century during Spanish colonial times. The original instrument had 4 single strings tuned A E A D.
It is believed that the cuatro's major influence as an instrument are the vihuela, bandurria, and tiple (another puerto rican instrument evolved from the Spanish guitarrillo). Publications like "El Gibaro" (Manuel Alonso, 1845) describe the use of instruments like cuatro, tiple, guitar, and percussion during parties. The instrument's major evolution would happened during the end of the 19th century. Based on literature and photos of the era, we can see the change from 4 single strings to 4 double strings (8 total), and later 5 double strings (10 total) with a different tuning B E A D G. The size and shape also evolved into what is considered now the "modern cuatro", a five double strings instrument with a violin guitar shape body.
There you have it, to answer a simple question and describe the instrument, I always have to give a brief history lesson.
Cuatro is the name of the Puerto Rican national instrument that more than describing the present of the instrument, describe its origins. Its sound however, defines its future. I say this, because I usually have this history conversation at gigs not playing traditional folk music from Puerto Rico, (which is what I grew up playing and where the cuatro is the main featuring instrument), but playing music that the audience knows very well (like Santana, Mumford and Sons, Coldplay, Django Reinhardt, Al Di Meola) but with an instrument they have never seen or heard before but can't believe how well it fits in the music.
As a cuatro player "cuatrista", that is my goal, to make the cuatro belong in any song.