Who was the Fourth Man in the Furnace Walking with Daniel?

When Daniel's three companions, Shadrach, Meshach, and Abednego, refused to bow down to Nebuchadnezzar's golden statue, the Babylonian king was infuriated. He had the three men thrown into a fiery furnace. When Nebuchadnezzar saw a fourth figure walking with the three, and all were unharmed by the blazing fire, he was astonished (Daniel 3:25).