Adrian Willaert lived from 1490-1562. He was born in Flanders, Belgium. He begin work in Rome around 1515 for Cardinal Ippolito I d'Este. Willaert then became director of music at St. Marks Church in Venice. This happened around 1527. He remained in Venice until his death. He composed motets and was a member of the so called Franco-Flemish Generation that wrote Motets. He used plainchant as the source for some of his text.
Willaert's music was composed through an entirely new process. He decided to write the music to follow the words, instead of bending words to fit music, as had been done since the rise of the Gregorian Chant. He was one of the first composers to demand that the syllables be printed in line with the notes they were sung on. A typical piece by him is "O crux, splendidor." The words fit with the notes, and he uses deceptive cadences extensively.
The deceptive cadence is a cadence that sounds like it will resolve, like the end of a John Williams piece. Instead of resolving the dissonance, Willaert continued the music. This gave a rising sense of tension. He also sought to preserve the modal structure of music used since the rise of Christianity. He did this by keeping the pieces in their original modes, but giving them depth and an emotional crescendo by adding a flat, which raised the mode of the piece a fourth (See circle of fifths).
This information was found in my IB music class notes and in chapters 6 and 7 of the History of Western Music, Grout, 6th ed.