Friedrich Nietzsche (1844-1900)
Nietzsche was originally inspired by Schopenhauer, but came to reject the idea that the will to live is fundamental. Instead Nietzsche believed in the will to power.
He also rejected Schopenhauer's Kantian belief in absolute truth. According to Nietzsche, there is no absolute truth. Any belief can be true only from some perspective. This view is called perspectivism. All science, religion, and philosophy is an expression of some particular perspective that its proponents try to get others to accept because of their will to power. All teachers seek converts and followers. Nietzsche wanted leaders, not followers.
The multiplication of churches after the Protestant reformation, and the variety of new scientific theories that contradict traditional Christian teaching, along with our modern faith in science, have made serious religious faith impossible. "God is dead."
Without God, we need new values. We cannot go back to the ancient master morality of good (understood as success, power, strength, etc.) versus bad (i.e. failure, weakness, etc.). This now strikes us as too crude to be plausible. But nor can we keep the resentful slave morality of the Jews and Christians, who twisted the master morality into one of good (i.e. failure, weakness, humility, meekness, poverty, chastity, etc.) versus evil (i.e. power, wealth, etc.). We must go beyond good and evil.
For this we need a new kind of person, an Overman or Superman. The Overman will be contemptuous of all that is ugly in himself or others, and will be happy, creative, living according to his own ideas, taste, and values.
The ultimate test of whether you are satisfied with the life you have made for yourself, of whether you have done your job properly, is to imagine an eternal recurrence of your life just as it has been in every detail. If you would rejoice at such a fate, you have got it right. This love of life is called amor fati.
Click here for a much longer summary of one of Nietzsche's book: The Twilight of the Idols.