Regina Isabel Luisa Pacini Quintero (January 6, 1871 – September 18, 1965) was a Portuguese lyric soprano, and First Lady of Argentina as the wife of Marcelo Torcuato de Alvear.

[2] Her father was the Italian baritone Pietro Andrea Giorgi-Pacini; her mother was Felisa Quintero.

[citation needed] In 1899, Pacini performed at the Teatro Solis, Montevideo, and the Politeama Theatre, Buenos Aires.

It was at the Politeama Theatre that she met Marcelo Torcuato de Alvear, the future president of Argentina (1922-1928).

[citation needed] The new century brought performances for Pacini in different Italian theaters, including San Carlo, Naples, and La Scala, Milan.