Author of "Father supreme! Thou high and holy One" in A Book of Hymns for Public and Private Devotion. (10th ed.) 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.
Anonymous