An obscurantist willfully withholds special knowledge from others.
There are two primary cultural connotations of this word, coming out of the European tradition. One is where the actor considers the knowledge too powerful or expensive for others, a form of elitism, expressed in both technical guilds and the Platonic philosopher king/tyrant who 'knows better'.
The other form is in making ones words hard to understand, either to hide emptiness or vagueness, a complaint against some philosophers (Hegel, Wittgenstein), or to hide simplicity behind technical language.