TSK · Mark 9:11

"Behold, I send my messenger, and he will prepare the way before me; and the Lord, whom you seek, will suddenly come to his temple; and the messenger of the covenant, whom you desire, behold, he comes!" says Yahweh of Armies.

If you are willing to receive it, this is Elijah, who is to come.

Elijah and Moses appeared to them, and they were talking with Jesus.