Nihilists

The Bleak Cabal or Madmen, who believe that there is no meaning in anything, but you can find the true meaning in yourself. This simultaneously tends to make them both the craziest-seeming people in Sigil after the Chaosmen while also being the sanest and often kindest. Their members can represent both crushing nihilism or hopeful anti-nihilism. As such they are immune to morale effects, insanity and mood altering spells tvtropes.org, Planescape (Tabletop Game)