"Guru." Forget the explanation; I just hate this one. (If you respond positively to "guru," I would love to know why.) I also hate "sage," "connoisseur," "guerilla," "whiz," "ninja," and other allegedly clever descriptors. Don't be clever for clever's sake.
Read the above article, and think about how you describe yourself.
Every writer is a self-promoter, no matter how much it makes you wince.