In a place where a big religious majority reigned, quite a lot of people believed what religious leaders told them, and they followed all kinds of superstitious beliefs, attributing things to divine action. They thought they had a soul that would survive death, or so they were told.
But then came a philosopher who challenged that with a strong skepticism. He told people, don’t believe something because it’s in scripture, or because your religious leaders tell you it’s true - only believe what you can verify for yourself to be true. He also told them that things didn’t happen because of divine providence, fate, or randomness, but because of cause and effect. He said all things that happened did so because of the conditions that lead to them. And he went further. He told people that they themselves were the product of these conditions and causes, their minds were the sum of many different faculties and functions, and they had no permanent self.
When people asked him, “What about the ultimate cause of existence?” or, “What about the afterlife?” he answered that those questions were not important to having a happy life, and they were not necessary to relieve their pain, worries, and suffering. He himself had tried both luxurious wealth and strict religious self denial, and none of it had delivered what it promised.
Instead, he taught them practical ways to calm themselves, focus their attention on positive things, practice moderation, be more aware of their world, be more mindful of their destructive emotions and handle them better, and develop their empathy to be more compassionate to one another. People only imperfectly practiced what he taught, and over time a lot of other ideas (some he would likely oppose) were layered on top of his views as they spread into many cultures.
Nevertheless, he did all this without ever reading Socrates or any others from his academy, without the compassionate examples of Gandhi or Jesus, without the ethics of Kant, without the rational or scientific methods discovered during the Enlightenment, and without the benefit of modern neuroscience (which is now studying his methods). That’s because he did this 2,500 years ago.
This skeptical heretic was named Siddhartha Gautama, and for his wisdom he was called the enlightened one, or ‘the Buddha’.