Heinrich Isaac (also known as Henricus, Arrigo d'Ugo, and Arrigo il Tedesco) (around 1450 ? March 26, 1517) was a Franco-Flemish composer of the Renaissance. He is regarded as one of the most significant contemporaries of Josquin des Prez, and had an especially large influence on the subsequent development of music in Germany.
Little is known about Isaac's early life, but it is probable that he was born in Flanders. It is known that he was writing music by the mid 1470s, and the first documentary reference to him is from 1484, when he was court composer at Innsbruck. The following year, he entered the service of Lorenzo de' Medici at Florence, where he was organist, choir master, and teacher to Lorenzo's children; he assumed this post on the death of Antonio Squarcialupi. One of his students in Florence was the future Pope Leo X. In 1494, the Medici were banished from Florence; the era of Savonarola was beginning, and Isaac was left to find employment elsewhere. However, he had married a Florentine and so maintained a household there throughout the remainder of his life.
By 1497, Isaac was in the employ of Emperor Maximilian I. He travelled widely in Germany, and is credited with having a big influence on German composers of the time. In 1502, he returned to Italy, going to Florence and then Ferrara, where he competed with Josquin for employment: a famous letter from the agent of the d'Este family compared the two composers, saying that 'Isaac is of a better nature than Josquin, and while it is true that Josquin is a better composer, he only composes when he wants to, and not when asked; Isaac will compose when you want him to.'