José António Carlos de Seixas (1704–1742) was a pre-eminent Portuguese composer of the early 18th century. An accomplished virtuoso of both the organ and the harpsichord, he succeeded his father as organist of Coimbra Cathedral at the age of fourteen. In 1720 he moved to Lisbon to serve as organist of the royal chapel, one of the highest musical posts in Portugal, which earned him a knighthood.

Seixas left several hundred keyboard sonatas that sit in an ambiguous transitional zone between the learned 17th-century style and the emerging galant idiom, making him a key figure in early Iberian keyboard music and a frequent source for guitar transcriptions.

Sources:

• https://en.wikipedia.org/wiki/Carlos_Seixas