John Calvin, 1509-1564, ministry began in 1529.
Both some history of John Calvin and many of his works can be found here: www.ccel.org/c/calvin
John Calvin is perhaps the most well known and influential of protestant figures next to possibly Martin Luther.
In popular history John Calvin is remembered as the popularizer of the doctrine of predestination. But this trivializes his teachings considerably to cast him in this light.
Unlike some other figures, John Calvin is complex and cannot be summarized easily in a few paragraphs. His life was filled with turmoil, and his doctrine was deployed not just as doctrinal papers, but in the life of the City of Geneva, where his teachings became law for many years.
The experiment of Geneva, as I like to think about it, is highly educational, as well has historically significant. As Calvin was essentially Presbyterian in his church structure, several firsts came out of this. The concept of elected leadership (rather than birth right) saw its first major instantiation here. To call John Calvin the father of western democracy is only a small stretch. The humanists of his day came to support these ideas (without the religious attachments) so western democracy was an idea whose origins can be traced to this period. They did not invent it completely however, as the Greeks (Athens) also had a form of democracy, but the resurgence in this form of government in our time is traceable to this period.
Primarily the Geneva theocracy enforced a rigid moral code, and it enforced its religious beliefs on all those it came in contact with.
The reason I call it an experiment is that it had its excesses. Just as the Catholic church persecuted and executed those who defied its teachings in the regions where it had control, so did the government of Geneva, although to their credit they recanted of this behavior later.
Lest you think Calvin was a monster, let me point out that this behavior was not out of the ordinary for the times, considering the sheer carnage the legacy of Romish thinking had produced. So today we draw from what Calvin did in theology, without proclaiming today that a theocracy is what Christianity must advocate or become.
The scale is different however, Calvin executed one person compared to the Catholic Church's 50 million over its thousand years of dominance, that is over 100 people a day sustained for ten centuries. That is more people killed than for any other 'ism, (although abortionism in America will pass it soon). Fascism killed its few millions, communism has collectively killed over 20 million, Saddam arguably killed about one million, and abortionism is over 20 million in second place.
The thinking that caused this behavior is a mistaken idea that the Church of Christ was an institution whose purpose was to rule politically with the full authority of Christ delegated to it. Calvin held this view just as strongly as Rome did.
The idea that the church is a voluntary association of believers did not (re)gain acceptance until much later in the reformation. The earliest reformation group to hold this viewpoint were the Anabaptists who were persecuted as vigorously by the early reformers as they were by Rome (many Anabaptists died, killed by both sides).
The early reformation period, especially reflected in the history of Britain, was characterzied by monarchs who swayed toward Catholicism, and then a successor leaned towards Protestantism, and then swung back again. During those swings they used tactics that today we would consider quite draconian.
By the 1700's, after two centuries of such abuse from reformers and over 1200 years of abuse from Rome, the idea of freedom of religion from state control and enforcement had taken hold, and indeed the birth of our nation was founded upon that very premise. All of Calvin's later followers, including Jonathan Edwards, George Whitfield, and Charles Spurgeon, held this view, which is similar to what we believe today, and were self-proclaimed Calvinists.
If you want to read a long detailed theological discourse on the roots behind this issue see John G. Reisinger's series of articles on the Ekklesia.
On a more positive note, the core doctrine of Calvinism as it endures today is best expressed by the following verses:
eph 2:8 For by grace are ye saved through faith; and that not of yourselves:
it is the gift of God:
eph 2:9 Not of works, lest any man should boast.
Calvinism can be best expressed as the idea that man is neither willing nor able to come to God on his own, and is totally sinful without either common grace (given in some measure to all as a restraining force against sin) or special grace (also known as saving grace) given only to those who have been saved. In this Calvin almost precisely echoes Luther (they are quoting the same verse of scripture after all), but Calvin develops this doctrine to a much higher level.
A proper Calvinist does not deny free-will, but says merely that it is limited in both its scope and ability to choose. As the Bible casts us as either slaves of the Devil or servants of God this is not an unreasonable thing to do. Lack of ability to choose God on our own also in no way absolves us of guilt for our sins.
John Calvin developed his thinking considerably farther than that however. All of history and of existence was seen in the light that God is sovereign, and that all things happen according to His will. The idea of the permissive vs the perfect will of God came out of this kind of thinking to avoid blaming God for planning the fall of man and sin, and things like that.
Calvinism gone too far, or perhaps cast in a bad light by its critics, says that we are entirely devoid of free will, and that God determines all. Thus nothing we do or say makes any difference. (Note: I later learned that Calvinists brand those who go too far in this and other areas as Hyper-Calvinists).
The great Calvinists that followed after Calvin certainly did not hold this view at all, as they were highly evangelistic, and understood our limited free-will clearly.
Personally I think if you stick with the doctrine of salvation by grace you can't go wrong, but the other stuff, if you want to get more depth in your education, is worth investigating.
One of the principal benefits of the doctrine of salvation by grace alone, is the understanding that once one is truly saved, one cannot lose it, or rather one will not fall away in unbelief. And since Jesus said all those who come to Him he will in no wise cast out (John 6:37) assurance of eternal security is merely the fact you believe the Gospel and want salvation (enough to obey Christ) and have a proper understanding of the cross and of who God is. Because these things are the gifts of God's grace, the fact that you have them is your evidence of eternal security.
A necessary consequence of this doctrine is that not all people who think they are saved really are, and that those who fall away in appearance were never truly saved in the first place.
Another consequence is that getting truly saved is not as easy as saying a quick prayer. A heart change, and a genuine committment to Christ are the necessary evidence of a true conversion. All the great Calvinists taught on this theme, and they often focussed on revealing false conversions in the hearts of those who heard them speak.
I have had a lot of time to think about this, and have concluded that the Bible supports Calvinism more than it supports Arminianism. I don't think this is an easy subject to cover either, as in my mind this is one of the most difficult and contentious doctrines in Christianity. Unfortunately it is also a really important one, so you can't just sweep it under the rug and ignore it. Perhaps some of my thinking on this will help:
Casting an argument in the proper light is necessary to judge the truth properly. It wasn't until I realized that the argument about Calvinism is really about the doctrine of salvation by grace, through faith, alone, which is easy to prove, that I became convinced.
If you get mired down in pre-destination vs. free-will, and did God plan the fall in advance, and so on, you can get lost in the forest real quickly.
The famous TULIP part of Calvinism came not from John Calvin at all, but from his immediate successors when they were trying to refute the five points of Arminianism, which were themselves intended to be five criticisms of Calvinism. Nevertheless TULIP accurately covered the major issues so it remains popular today.
I will cover the TULIP doctrine in my writeup on Jacobus Arminius, since he was really the catalyst for it.