From the 5th century to the 15th century, a spiritual darkness gripped the world. This period of time was known as the Dark Ages (sometimes also known as the Middle Ages), and was a time of war, disease, and famine. Centuries before this time, God's own Son, Jesus, the light of the world, had come to offer his life for the sins of mankind. But now the true Church, the one set up by Jesus, had been persecuted horribly and driven underground. So the greatest problem for the people who lived in this period was not their suffering. It was Satan's spiritual deception—the Catholic Church which had come to dominate the world, masquerading as Christ's true Church.
During the Dark Ages, the Bible was only viewable by priests, and then only the most highly educated ones could even understand it. But, from about 1400-1550, some brave men started smuggling Bibles into Europe and other countries, and translating the Bible into different languages. This was called the Reformation.
John Wycliffe, John Huss, William Tyndale and others also played important parts in the Reformation, but Martin Luther is the one that we know best today, because of the dramatic thunderstorm, the 95 Theses, and his part in God's plan to pierce the spiritual darkness of the Catholic Church, letting the light of God's truth into the world.
The Reformation (a short paper on the Reformation by my older son)
"Luther" - the full length movie available at Amazon
The Reformation: Post Tenebras Lux