In 2 Nephi 3:18-19 we find the following:
And the Lord said unto [Joseph of Egypt] also: I will raise up unto the fruit of thy loins; and I will make for him a spokesman. And I, behold, I will give unto him that he shall write the writing of the fruit of thy loins, unto the fruit of thy loins; and the spokesman of thy loins shall declare it.
And the words which he shall write shall be the words which are expedient in my wisdom should go forth unto the fruit of thy loins. And it shall be as if the fruit of thy loins had cried unto them from the dust; for I know their faith.
According to Robert Millet, traditionally this passage (2 Nephi 3:18-19) has been interpreted in terms of Joseph Smith being given a spokesman, either Oliver Cowdery (D&C 28:3) or Sidney Rigdon (D&C 100:9-11; 124:104). More recently, however, Elder Bruce R. McConkie has provided an alternative explanation: the person of the lineage of Joseph who would be raised up to write the record of Joseph (the Book of Mormon) is Mormon; the spokesman of the word is Joseph Smith (see McConkie, New Witness 426). [Robert L. Millet, “The Influence of the Brass Plates,” in Nyman and Tate eds. The Book of Mormon: Second Nephi, The Doctrinal Structure, p. 220]