D&C 77

The Prophet Joseph Smith was asked -

Q. What are we to understand by the angel ascending from the east, Revelation 7th chapter and 2nd verse?
(Doctrine and Covenants | Section 77:9)

He answered -

"We are to understand that the angel ascending from the east is he to whom is given the seal of the living God over the twelve tribes of Israel; wherefore, he crieth unto the four angels having the everlasting gospel, saying: Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads..."  (Doctrine and Covenants | Section 77:9)

In my mind, this means until Israel is gathered and receives the sealing power of ordinances, oaths, and covenants for the Prophet adds -

"...And, if you will receive it, this is Elias which was to come to gather together the tribes of Israel and restore all things."  (Doctrine and Covenants | Section 77:9)

We learn that Elias signifies a gatherer or preparer and can be many people.  In a sense, Elias could be all those that participating in the preaching the gospel and gathering Israel.