CHA CHA CHA 

The inventor of the musical genre cha-cha-chá was a violinist and composer named Enrique Jorrín, whose song La Engañadora (1951) is considered to be the first cha-cha-chá ever composed (Orovio 1981:130-1).
From the beginning (that is to say, the later stages of development of the danzón-mambo), the composers and interpreters of cha-cha-chás had a symbiotic relationship with the dancing public:
"What Jorrín composed, by his own admission, were nothing but creatively modified danzones. The well-known name came into being with the help of the dancers [of the Silver Star Club in Havana], when, in inventing the dance that was coupled to the rhythm, it was discovered that their feet were making a peculiar sound as they grazed the floor on three successive beats: cha-cha-chá, and from this sound was born, by onomatopeia, the name that caused people all around the world to want to move their feet..." (Sanchez-Coll 2006)
The "three successive beats" are the "1-2-3" steps, as counted in Cuba (see below).
The cha-cha-chá begins on the fourth beat of a measure of 4/4. Cuban dancers count it "1-2-3, 1-2."