Francisco Tarrega (1852-1909) was a Spanish composer and classical guitarist regarded by many as "the father of the classical guitar." Adelita is a mazurka originally composed for guitar by Tarrega. The mazurka originated in Poland and was popularized by Frederic Chopin.
The tempo is indicated as Lento, but seems to work better at a faster tempo. The audio file here is at 80 bpm. However, this piece should not be performed metronomically, but rather with a more rubato style.