crypto-geek
One who hides "nerdy" interests while maintaing an outwardly "normal" appearance, esp. someone who one would not expect to pursue such interests, such as a jock. A crypto-geek would usually be embarassed if these interests were revealed to his or her main circle of associates.
I didn't realize John was a crypto-geek; who would have thought the captain of the football team plays Dungeons and Dragons?