In 1597 a king wrote book about witches who was he?

The king you're likely thinking of is King James VI of Scotland (who later became King James I of England).

He published a book called "Daemonologie" in 1597. It was a treatise on witchcraft, demonology, and the nature of evil.

This book was very influential in shaping the view of witchcraft in England and Europe during the 17th century.