Events that occurred on 21 October.
 On Earth
- 1925 – J.R.R. Tolkien submits his resignation from Leeds, his employment will officially end on 31 December 1925.
- 1927 – J.R.R. Tolkien writes a letter to Willard G. Harding.
- 1929 – Author Ursula K. Le Guin born.
- 1955 – J.R.R. Tolkien presents his paper English and Welsh.
- 1963 – J.R.R. Tolkien writes a letter to Mrs. Munby.
- 1972 – Actor Felix Felton dies.
- 2004 – The 50th Anniversary Edition of The Lord of the Rings is published.
- 2008 – Fantasy novel The Indigo King, featuring J.R.R. Tolkien as a fictional character, is published.
- 2010 – In a press release, it is confirmed that Martin Freeman will play Bilbo Baggins in The Hobbit (film series).