Not only a comedian/actor/writer but also a fine medievalist who engaged in original scholarship. Some years ago he caused quite a stir in Chaucerian circles by arguing that the Knight in the Knight's Tale (Canterbury Tales) was not actually the ideal of a knight but rather a mercenary and further, that the Knight's Tale, rather than being an ode to chivalry, "emerges...as a hymn to tyranny, dressed-up in the rags of a chivalric romance."[0] This sounds fairly minor but it's an interpretation, albeit one not wholly accepted by many scholars, that upended centuries of scholarship. An impressive achievement.
[0] http://smuhlberger.blogspot.com/2007/03/chaucers-knight-by-t...