Which prophet warned the people of Nineveh about God's impending judgment?

The prophet who warned the people of Nineveh about God's impending judgment was Jonah.
Jonah was a prophet from Israel who was instructed by God to go to the city of Nineveh and deliver a message of repentance. However, Jonah initially tried to avoid this responsibility by boarding a ship headed in the opposite direction. In response, God sent a great storm that endangered the ship, and Jonah admitted that he was running away from his divine calling.
After being thrown overboard by the ship's crew, Jonah was swallowed by a large fish and remained in its belly for three days and three nights. During this time, Jonah prayed to God and repented for his disobedience. Eventually, the fish vomited Jonah onto dry land, and he decided to fulfill God's command.
Jonah finally arrived in Nineveh and proclaimed God's message to the people. He warned them that if they did not repent and turn from their wicked ways, the city would be destroyed in forty days. The people of Nineveh, including the king, took Jonah's message to heart and repented, fasting and wearing sackcloth as a sign of their remorse. Their actions moved God, and He decided to spare Nineveh from destruction.
In summary, Jonah was the prophet who warned the people of Nineveh about God's impending judgment. Through his reluctant obedience, the city of Nineveh was given an opportunity to repent and escape God's wrath.