In some hymnals, the editors noted that a hymn's author is unknown to them, and so this artificial "person" entry is used to reflect that fact. Obviously, the hymns attributed to "Author Unknown" "Unknown" or "Anonymous" could have been written by many people over a span of many centuries. Go to person page >
Almighty Maker, Lord of all. [Holiness.] This hymn is given in J. H. Thom's Unitarian Hymns, Chants & Anthems, 433, as from "Rees's Collection," i.e. Kippis's Collection of which Abraham Rees was one of the editors, 1795: No. 206, where it is given as from "Select Collection of 1756."
-- John Julian, Dictionary of Hymnology (1907)