Samuel Taylor Coleridge

In his early twenties, crossed in love, Coleridge ran away from Cambridge and joined the 15th Light Dragoons.... One day, as he was on sentinel duty, two officers walked past, chatting about Euripides; one of them quoted a couple of lines. Begging their honours' pardon, the sentinel corrected the Greek and observed that the lines actually came from Sophocles. The astonished officers had him transferred to the regimental hospital as an orderly....

Before long (Coleridge's) friends secured the trooper's discharge by means of a sweetener of around 25 English pounds and on a technical doubt about his sanity. (D.J. Enright, Play Resumed, 1999)