In the past, people used the term great king for leaders of major military powers. It later became a common title for Assyrian kings.
What is the basis of this confidence of yours?: The Assyrian officer claimed that Jerusalem's citizens would be unwise to trust Hezekiah's words, given Assyria's strong military. Seeking help from Egypt would also be unwise. The chief of staff argued that trusting in the Lord was also a mistake. The officer might have hoped to win over citizens who had worshiped at the shrines and altars Hezekiah had destroyed.