Prophet Brigham Young (1801 - 1877):
“Angels are those beings who have been on an earth like this, and have passed through the same ordeals that we are now passing through. They have kept their first estate far enough to preserve themselves in the Priesthood. They did not so violate the law of the Priesthood and condemn themselves to the sin against the Holy Ghost as to be finally lost. They are not crowned with the celestial ones. They are persons who have lived upon an earth, but did not magnify the Priesthood in that high degree that many others have done who have become Gods, even the sons of God.”
- Prophet Brigham Young, Journal of Discourses, v. 9, p. 103; online at Link is here.
Apostle Parley P. Pratt (1807 - 1857):
“Angels are of the same race as men. They are, in fact, men who have passed from the rudimental state to the higher spheres of progressive being. Some have died and risen again to life, and are consequently possessed of a divine, human body of flesh and bones, immortal and eternal. They eat, drink, sing and converse like other men. Some of them hold the keys of Apostleship and Priesthood, by which they teach, instruct, bless, and perform miracles and many mighty works. Translated men, like Enoch, Elijah, John the Apostle, and three of the Apostles of the Western Hemisphere, are also like angels. They are ministers, both to men upon the earth, and to the world of spirits. They pass from one world to another with more ease, and in less time than we pass from one city to another. They have not a single attribute which man has not. But their attributes are more matured, or more developed, than the attributes of men in this present sphere of existence.”
- Apostle Parley P. Pratt, Key to the Science of Theology, p. 112; online at Link is here.
LDS Historian B.H. Roberts (1857 - 1933):
“What are angels? They are intelligences of the human species. Many of them are offsprings of Adam and Eve. That is they are men, who have, like Enoch or Elijah, been translated; or, like Jesus Christ, been raised from the dead; consequently they possess a material body of flesh and bones, can eat, drink, walk, converse, reason, love, fight, wrestle, sing, or play on musical instruments. They can go or come on foreign missions, in heaven, earth, or hell; and they can travel space, and visit the different worlds, with all the ease and alacrity with which God and Christ do the same, being possessed of similar organizations, powers and attributes in a degree.”
- B.H. Roberts, LDS Church Historian, Mormon Doctrine of Deity, p. 256; online at Link is here.