Siddhartha Gautama was a prince who was brought up in his father’s palace in Northern India in the 5th Century BCE, where the religion was Hinduism. He lived a life of luxury and his father protected him from the world. One day, he left the palace for the first time and saw four sights:

An old man - this showed that we all decline physically.
A sick person.
A dead body.
A holy man - he was an ascetic who lived a very simple life of self-denial. He was trying to understand the world.

These sights made him realise that there is much suffering in the world and he decided to dedicate his life to seeking the truth. He secretly left the palace in the middle of the night, leaving behind his wife and young son.

Y9 Buddhism

The Four Sights