Short answers, pulled from the story.
William Byrd (c. 1540-1623) was an English Renaissance composer widely regarded as one of the greatest composers of the Renaissance. He is often grouped with John Dunstaple and Henry Purcell as one of England's most important composers of early music, and he wrote in nearly every musical form current in England, from sacred polyphony to keyboard music to consort songs.
Byrd was raised in a Protestant family but became a Roman Catholic from the early 1570s onward. His wife Juliana was cited for recusancy in 1577, and Byrd himself appeared in recusancy lists from 1584. He paid heavy fines for non-attendance at Anglican services throughout his life while continuing to write Catholic sacred music, including three Mass cycles and the two-volume Gradualia.
The Cantiones sacrae of 1575 was a joint publication by Byrd and Thomas Tallis collecting 34 Latin motets, 17 by each composer, dedicated to Queen Elizabeth I. It was the first use of their royal monopoly on music printing. The collection was a financial failure, and by 1577 Byrd and Tallis were petitioning the Queen directly, writing that it had "fallen oute to oure greate losse."
My Ladye Nevells Booke is a manuscript collection of 42 keyboard pieces by Byrd, completed by the scribe John Baldwin on the 11th of September 1591. It was probably produced under Byrd's supervision and dedicated to Lady Elizabeth Neville, wife of Sir Henry Neville of Billingbear House, Berkshire. The collection includes pavans, galliards, variations, and programme music such as The Battle and The Barley Break.
Scholars including Joseph Kerman have identified a persistent layer of coded meaning in the motet texts Byrd chose during the 1580s, with recurring themes of persecution, captivity, and deliverance that appear to reflect the situation of England's persecuted Catholic community. His three Mass cycles were published without dates or printer's name, in editions designed for easy concealment, because possessing heterodox books was still dangerous.
William Byrd died of heart failure on the 4th of July 1623 at Stondon Massey in Essex, where he had lived since around 1594. His death was recorded in the Chapel Royal Check Book in a unique entry describing him as "a Father of Musick." He died a wealthy man, with rooms at the London home of the Earl of Worcester.