The Cuco (or Coco) is a mythical monster, a ghost, witch; equivalent to the boogeyman found in many Hispanic and Lusophone countries. He can also be considered a Hispanic version of a bugbear, as it is a commonly used figure of speech representing an irrational or exaggerated fear. The coco is a male being while coca, or cuca are the female versions of the mythical monster although it is not possible to distinguish one from the other as both are the representation of the same being.
Names and etymology
The myth of the coco originated in Portugal and Galicia. According to the Real Academia Española the word "coco" derives from the Portuguese language, and referred a ghost with a pumpkin head (in which "coco", from whitch derives coconut, is analogous to a pumpkin orcalabaza). The word coco is used in coloquial speach with the meaning of head either in portuguese or spanish. The word "cocoruto" means, in portuguese, the top of the head. The name coco could be related to the old Celtic root *kokk– meaning ‘red’.  Either the pumpkin or the dragon are related with the fire of the same color. Koko in Basque has the meaning of mask. 
In Northern New Mexico and Southern Colorado, where there is a large Hispanic population, el cuco is referred to in its Spanglish name, the Coco Man. But in Brazilian folklore, the typical monster sung in children rhymes is Cuca, pictured as a female humanoid alligator from Portuguese coca, a dragon.
The legend of the Cuco is widely used by parents in Spain and Latin America in order to make their children go to sleep. Parents sing lullabies or tell rhymes to the children warning them that if they don't sleep, el coco will come and get them. The rhyme originated in the 17th century has evolved over the years, but still retains its original meaning. The following is an example of one popular version of the rhyme, sung with the "Rock-a-bye Baby" rhythm:
|“||Duérmete mi niño, duérmete ya…
Por que viene el coco y te comerá.
Which translates as:
|“||Sleep my child, sleep now…
Or else comes the coco to eat you.
During the Portuguese and Spanish colonization of Latin America, the legend of the cuco was spread to countries such as Mexico, Argentinaand Chile. In the Mexican-American community the creature is known as "El cucuy".
There is no general description of the cuco, as far as facial or body descriptions, but it is stated that this being is extremely horrible to look at. The coco is variously described as a shapeless figure, sometimes a hairy monster, that hides in closets or under beds and eats children that misbehave when they are told to go to bed. In its "sack man" incarnation, the cuco is portrayed as an adult male, usually in the form of a bum, or a hobo, who carries a sack on his back (much like Santa Claus would), and collects mean disobedient children to sell. Parents may tell their kids that they will call the sack man to collect them if they do not behave. The sack man also exists in Spain in the form of the Hombre del Saco or Hombre de la bolsa, and is usually depicted as a mean and impossibly ugly and skinny old man who eats the misbehaving children he collects. In Brazil the cuco appears as a female, 'cuca'. Cuca appears as the villain in some children books by Monteiro Lobato. Artists illustrating these books depicted the cuca as an anthropomorphic alligator. This is an allusion to coca the dragon, from the folklore of Portugal and Galicia. Traditionally, however, the coco, is represented by a carved vegetable lantern made from a pumpkin with two eyes and a mouth, that is left in dark places with a light inside to scare people. The name of the "coconut" derived from "coco" and was given to the fruit by the sailors of Vasco da Gama because it reminded them of this mythical creature.
According to social sciences professor Manuel Medrano, popular legend describes cucuy as a small humanoid with glowing red eyes that hides in closets or under the bed. 'Some lore has him as a kid who was the victim of violence … and now he’s alive, but he’s not,' Medrano said, citing Xavier Garza’s 2004 book Creepy Creatures and other Cucuys."
In popular culture
Dominican Salsa–Merengue musician and singer Cuco Valoy makes several humorous references to the myth in some of his songs (¡ahi viene el cuco, mama!). Puerto Rican musician Angel Peña also uses nickname is "Cuco", an allusion to the legend.
Cuco, the tequila-dispensing donkey resides at Casa Herradura in Gualajara, Mexico. He carries around mini barrels of el Jimador tequila for visitors who are touring the facility to sample.