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 >
It is finished! Shall we raise? [Good Friday.] The earliest work to which we have traced this hymn is A Collection of Psalms & Hymns for St. Mary's, St. Giles, and Trinity Churches, Reading. Reading: E.Havill, 1830. It is found in several modern collections, including Spurgeon's Our Own Hymn Book, 1866, &c.
--John Julian, Dictionary of Hymnology, Appendix, Part II (1907)