Zero
In college we had a freshman writing seminar requirement, which were encouraged to be broadly interpreted.  I took a Math course, of all things.  We learned Euclidean geometry, proved the Pythagorean theorem through construction, calculated ancient dates, and wrote about it all.My final paper was a 15-20 page paper on Zero, and, despite cringing at my own writing, is still probably my favorite thing I've ever written.  Zero has a fascinating history, from being outlawed in a few European countries, to being associated with the Mayan King of Death.  One great little piece is the following poem:>U 0 a 0, but I 0 thee>O 0 no 0, but O 0 me.>O let not my 0 a mere 0 go,>But 0 my 0 I 0 thee so.The word "cipher" used to be another name for zero/0, so the above reads as:>You sigh for a cipher, but I sigh for thee>O sigh for no cipher, but O sigh for me.>O let not my sigh for a mere cipher go>But sigh for my sigh, for I sigh for thee so.Which, of course, explains why Neo, The One from the Matrix, had an enemy named Cypher.