The messiah will not be an angel, but a human just like anyone else. However, his character will be saintly, and he will grow even further in his righteousness. When the time comes, he will become the redeemer and will be given the unique soul of the messiah.

The messiah will certainly be human, a righteous person who is born from a man and a woman. But on that day he will grow in righteousness…and then, on that day, at the very end, the soul of his soul, which has been kept in the Garden of Eden, will arrive and will be given to this righteous man, and he will then become the redeemer. (Rabbi Ĥayyim Vital, Arba Me’ot Shekel Kesef, p. 78)

Just as Moses did not know that he would be the one to redeem the children of Israel, until the time for the redemption came, the messiah, too, will not know that he is the redeemer. In every generation there is one who is worthy to be the redeemer should the time for redemption come and should that generation deserve to be redeemed.

The messiah will not be aware of his role until the time of the redemption arrives:

Regarding the coming of the son of David, I must explain that Moses, our teacher, who was the first redeemer, reached the age of eighty years old and did not know or sense that he would be the redeemer of Israel. Even when the Holy One, blessed be He, said to him, “Go and I will send you to Pharaoh” (Exodus 3:10), he refused and did not want to accept it upon himself. So too will it be, God willing, for the final redeemer.

In every generation there is a Jew who is worthy to be the messiah:

Once the Temple was destroyed, an individual was immediately born who was worthy, due to his righteousness, to be a redeemer, so that if the time were to come, God would reveal Himself to him and send him, and then the spirit of the messiah, which was concealed above until the time for its coming, would awaken in him. This is what we saw with King Saul after he was anointed: The spirit of sovereignty and the divine spirit, which he had not felt beforehand, came over him. This is how it was for the first redeemer, and this is how it will be for the final redeemer, and the righteous one himself will not know [until that time that he is to be the redeemer]. Due to our many sins, numerous potential redeemers have already died and, although they were worthy, we have not merited that the spirit of the messiah was awakened in them, because the generation was not worthy. But when the time comes, God willing, God will reveal Himself to him as He did to Moses at the burning bush, and He will send him [to redeem the Jewish people]. (Rabbi Moshe Sofer, Responsa Ĥatam Sofer 6:98)