Johnny Alf, 80, a founder and pioneer of Bossa Nova music and a pianist artist, died Thursday at a hospital near Sao Paulo, Brazil, of multiple organ failure. He had been fighting prostate cancer. Mr. Alf, who widely influenced later stars, was called the "true father of Bossa Nova" by Ruy Castro, who wrote a definitive history of the music.  Mr. Alf, born Alfredo Jose da Silva in Rio de Janeiro, was an aficionado of early American jazz, which greatly influenced his work and that of Bossa Nova as a whole.