The origins of Brazilian football are rooted in slavery. As the game gained popularity in the South American continent, it finally opened its doors to black Brazilians. The black population was mostly illiterate, and therefore, most players were unable to write their own names. Some teams sent their black players to writing classes, while others, would simply give their players a shorter name, so at least they would be able to sign their own autographs. Therefore, a player that had a long, complicated surname would simply become “Silva”. This explains the evolution of nicknames in modern football where names like “Ronaldo”, “Kakà, “Fred”, and “Pelé” are the norm.
Source: Futebol: A Brazilian Way of Life – By Alex Bellos