Cavaquinho.

Ernesto Júlio Nazareth (1863 - 1934) was a Brazilian composer and pianist, especially noted for his creative tango and Choro compositions.
Samba first appeared as a distinctive kind of music at the beginning of the 20th century in Rio de Janeiro (then the capital of Brazil) under the strong influence of immigrant black people from the Brazilian state of Bahia.
Samba is characterised by a syncopated 2/4 rhythm with a muted beat and a main beat, usually played by a surdo (bass drum) or tan-tan.
Another important element is the cavaquinho, also known as cavaco, a small four-stringed instrument of the guitar family brought by the Portuguese: Hawaiian ukulele is a derivative.
The cavaquinho is the connection between the harmony section and the rhythm section; its presence usually differentiates real samba from softer variations such as Bossa Nova.