(Today's his death day, actually.)
The guy in the picture is Martin Luther, not to be confused with Martin Luther King or Martin Luther King, Jr. Those two were named after him.
Martin Luther was going to be a lawyer, but quit college to become a Catholic monk. He then decided that the Pope wasn't interpreting the Scriptures correctly. He was sent to Rome to deliver some letters, and was
absolutely appalled at the practice of Indulgences.
An Indulgence is the full or partial pardon of sins, which occurs when gazing on relics, paying for pieces of paper, saying the Lord's Prayer while climbing some steps, and a lot of other acts like that. Luther said that by doing those, you are depending on yourself and not on Jesus Christ to save you. He wrote 95 Thesis and hung them up on the Wittenburg Castle Church on October 31st, 1517.
He was called up before the Emperor for that, and asked to recant. Luther was prepared to give an answer, and so was allowed to come back at noon the next day. That was when he gave probably his most famous speech.
"Unless I am convinced by the testimony of the Scriptures or by clear reason (for I do not trust either in the Pope or in councils alone, since it is well known that they have often erred and contradicted themselves), I am bound by the Scriptures I have quoted and my conscience is captive to the Word of God. I cannot and will not recant anything, since it is neither safe nor right to go against conscience. May God help me. Amen."
The Catholic church declared him a heretic. That meant that he would be arrested and killed, like many other theologians for centuries. Luther was given safe passage back to Wittenburg, but Prince Fredrick didn't trust that.
Prince Fredrick kidnapped Luther (without the afor-mentioned lawyer-turned monk-turned outlaw) knowing. He stayed in an attic in the Wartburg Castle. While there, he translated the New Testament from Koine Greek into German so that plain old people could read it. He also wrote about a gazillion theological writings.
When Luther returned secretly to Wittenburg, he wrote in a letter, "During my absence, Satan has entered my sheepfold, and committed ravages which I cannot repair by writing, but only by my personal presence and [the] Living Word [of the Bible]." For eight weeks in Lent, he preached a sermon every Sunday that affirmed that what the Bible says is true.
Even though helping in Wittenburg had worked, people outside of that town were taking his writings and teachings too far. They were actually planning to attack the Roman Catholic church. Luther managed to keep them from doing it, but pointing out that we should love our enemies, and not hurt them.
Luther actually married a nun. Katharina von Bora and eleven others escaped from a nunnery in herring barrels. They moved into a former monestary, which was a gift from John the Steadfast. The two had six children, and were very poor. A few of the children died during their childhood.
He also wrote two catechisms, established a new church denomination, and made a new order of service (now called the Divine Service). The service was conducted in German so that everybody could participate. Luther wrote several hymns, and translated the Bible from Greek and Latin into German.
At the end of his life, he was extremely sick. Luther went to settle a dispute, and apparently died on the way home. Maybe the dispute was too noisy and it was just too much for him. He was buried in the same church he had been hidden in.