What do you call someone who has extensive knowledge but won't share it?

What do you call a person that has a lot knowledge/information but decides to not share it?

Is it really the classic know-it-all or enlightened?

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.

The phrases "information miser" and "miser of knowledge" have both seen some use.

A gatekeeper of information is someone who may have extensive knowledge and may choose not to share it, but it isn't a job requirement.

Maybe they're secretive or close-mouthed by nature.

Or perhaps they simply work for Apple.