"The Diary of an Old Soul" is a collection of 366 daily Christian devotional poems by Scottish author, poet, and Christian Minister George MacDonald. Known primarily for his fantasy works and fairy tales, MacDonald was heavily influenced in his life and his writings by theology. This influence can easily be seen in "The Diary of an Old Soul" as well as in many of his fictional works too.

George MacDonald (1824 - 1905) was a Scottish author, poet and Christian minister. He was a pioneering figure in the field of fantasy literature and the mentor of fellow writer Lewis Carroll. His writings have been cited as a major literary influence by many notable authors. C. S. Lewis wrote that he regarded MacDonald as his "master": "Picking up a copy of Phantastes one day at a train-station bookstall, I began to read. A few hours later," said Lewis, "I knew that I had crossed a great frontier." G. K. Chesterton cited The Princess and the Goblin as a book that had "made a difference to my whole existence".