Random Number God definition, from Internet Connection, Inc.

[rec.games.roguelike.angband; often abbreviated ‘RNG’] The malign force which lurks behind the random number generator in Angband (and by extension elsewhere). A dark god that demands sacrifices and toys with its victims. “I just found a really great item; I suppose the RNG is about to punish me...” Apparently, Angband's random number generator occasionally gets locked in a repetition, so you get something with a 3% chance happening 8 times in a row. Improbable, but far too common to be pure chance. Compare Shub-Internet.