Final answer:
Isaiah was the prophet during the reign of King Hezekiah, who is known for his religious reforms that emphasized the exclusive worship of Yahweh.
Step-by-step explanation:
The prophet at the time of King Hezekiah was Isaiah. Hezekiah reigned as the king of Judah from 727 to 697 BCE and is known for his religious reforms that sought to centralize worship in the temple of Jerusalem and to return to the worship of Yahweh exclusively. During this period, the Prophetic Movement, which called for the worship of Yahweh alone and adherence to the laws of Moses, was in full effect.
Prophets like Isaiah played a crucial role in guiding both kings and the people of Judah towards monotheism and away from polytheistic practices. The Biblical narrative praises Hezekiah's efforts to cleanse his kingdom of unauthorized worship, and it is under his rule—with the support of prophets such as Isaiah—that the Hebrews sought to reaffirm their covenant with Yahweh.