A Luddite is a person who is like Ned Ludd.
A Leninist is a person who follows the teaching of Lenin, which is different.

A Barzunite is a person who is like Jacques Barzun.
A Calvinist is a person who follows the teaching of John Calvin, which is different.

A Sadist is a person who is like the Marquis de Sade.
A Benedictine is a person who follows the teaching of St Benedict of Nursia, which is different.

These seem less than iron-clad distinctions, but I suspect that there truly is a worthwhile distinction lurking in here somewhere.