Isaiah takes one of his general images and makes it specific. Where the generalized image marked the whole. now the head and tail are used to mark specific people.
The "head" must be a ruler, though he is unnamed. it is probably Pekah, as the prophecies are directed to Israel. While Syria was a confederate, it is Israel who should have turned to their God, and yet turn away.
The prophet who tells lies is also not named, but again is probably a real person. Isaiah has previously noted that Israel is more willing to turn to soothsayers than to listen to a prophet of the Lord. It is possible that this reference is to a specific man who advised Pekah, and was considered to be a prophet. In Isaiah's eyes, however, he is no more than the soothsayers who speak lies that men want to hear.