According to the Old Testament, the prophet swallowed by a great fish was Jonah.
The Book of Jonah says that Jonah tries to flee from the divine command to go to Nineveh. He boards a ship, and a violent storm threatens the crew. Jonah tells the sailors that the storm is connected with his disobedience, and he is thrown into the sea. A great fish then swallows him, and Jonah remains inside it for three days and three nights.
Jonah prays from inside the fish before being released onto dry land. He then goes to Nineveh and announces its coming judgment. The people repent, and God spares the city, which frustrates Jonah. The book’s ending focuses on mercy and on Jonah’s limited understanding of compassion.
The text says “a great fish,” not specifically a whale. That distinction matters because later retellings often use “whale” as shorthand. Jonah is also sometimes called a minor prophet, meaning the book is short, not that the prophet was unimportant.