Kierkegaard is one of those thinkers who's almost more interesting as a personality
than as a philosopher
His father, Michael Kierkegaard, was brought up in great poverty in rural Denmark. At about the age of 10, Michael cursed God out of anger with his terrible condition--and not too long after, his rich uncle chose the boy as his sole heir for no apparent reason. Michael was taken to Copenhagen and groomed for a life of wealth. He enjoyed remarkable good luck in financial matters for the rest of his life, and so he became convinced that his material wealth was a reward from Satan for his decision to forsake God. To top it off, Michael ended up marrying a housemaid who he had knocked up.
As a result, young Soren got a lot of money and a lot of deep-rooted religious guilt. He completed seminary studies for the official Danish Lutheran church, but never took a post as a pastor. Since he was supported by his father, he didn't need to work and spent all his time writing and studying. His father convinced him that he would die young, and so he paid no attention to supporting himself. Instead,he spent hours writing and agonizing over religious issues, all the while maintaining the public appearance of a rich ne'er-do-well to avoid the possibility that he might be identified as a virtuous man.
When he was 22 he fell in love with a 12-year-old girl named Regine Olsen. He visited her often, and when she was 16, old enough to marry at the time, he officially began courting her. They were soon engaged, but after a few months he became convinced that he was unworthy of her and too brooding to ever be a good husband to her. Because he wanted to make sure that her reputation wasn't harmed by his decision to break off the engagement, he made a point of going out to bars and theaters so that the local society would think that he had fallen into a dissolute life. She wasn't fooled and tried to keep him , but he couldn't be swayed. He spent almost a year and Germany and came back, where he wrote in private and publically continued to live as an eccentric playboy.
Kierkegaard was concerned with ensuring that his Christian experience was sincere. He believed, probably correctly, that for most people religion was more a set of social conventions than a deep relationship with God. He described three types of interaction with God: aesthetic, which focuses mostly on outward demonstrations of social religion; ethical, which is based in following the moral code; and religious, in which a personal relationship with God transcends the bounds of society and ethics. This intensely personal and intimate vision is existentialist in that it calls for an intensely personal and deeply committed struggle with reality that allows one to go beyond the rules of society. He also hits on the existentialist themes of the fear and dread that a human faces when confronted with their own infinite freedom. A short and typically poetic examination of this process is found in Fear and Trembling, where Kierkegaard imagines and reflects on the thoughts of Abraham as he prepares for the binding of Isaac (see Genesis 22).
The end of Kierkegaard's life was marked by a powerful attack on the established Lutheran church in Denmark. He developed his plan over a series of years, and delayed his first publications for years because the aged archbishop of Copenhagen was a personal friend and former tutor. After that archbishop died, Kierkegaard waited six months for the new archbishop to settle in before letting loose with a stream of ferocious attacks on the state of Christianity. He crafted a series of articles and commentaries which began with the statement, "Christianity does not exist." Instead, Kierkegaard said, it had been replaced by Christendom, a socio-political structure that papered over the radical message of true Christianity. he wrote with such intensity that he became sick and died within months, leaving his few remaining goods to Regine.
Because Kierkegaard wrote in Danish it was many years before his works became widely known. However, today he is recognized as being in many ways ahead of his time--and he is even recognized as a saint in some parts of the Lutheran church that he attacked so viciously but politely in his own life.