The Prophet Natan is talked about in the second book of Samuel, Chapters 11 and 12, in the Old Testament.
One day while standing on the roof of his palace, King David spotted Batsheva, the wife of one of his soldiers, Uriah. To cut a long story short, she conceives his child, and he ends up arranging for Uriah to be placed on the front lines and for him to be killed. The plan works, and after Batsheva's period of mourning ends, King David marries her.
The prophet Natan then comes to King David with a problem. He tells the King of two men, one rich and one poor. The rich man had very large flocks and herds, but the poor man had only one lamb, which he cared for greatly. One day, the rich man received a traveller, but was loathe taking any of his own livestock to prepare a meal for the guest. So, he took the poor man's lamb and prepared it for the traveller.
Upon hearing this, the King flew into a rage. "As Hashem lives," he tells Natan, "the man who did this deserves to die." "Ata Haish," Natan responds, "you are the man!" Natan then explains how the King was the rich man, whom Hashem had blessed in numerous ways. His soldier Uriah, however, had been blessed with just one "lamb," his wife, Batsheva. King David answered Natan with just two words, "Hatati LeHashem - I have sinned before Hashem."
Natan was able to approach King David, the 2nd King of Israel and ancestor of the Moshiach (Messiah), and explain to him where he went wrong. This takes great courage and intelligence.
The Anglicised version of the Hebrew name "Natan" is "Nathan".