Diabolic characters are the cruel, heartless killers.  They are the kind
who plot and plan to harm others simply for their own entertainment.  This
does not imply that they do not have deeper goals, however.  Their goals
are usually products of insanity and are too convoluted for the normal
person to comprehend.  Diabolic people need not follow normal rules of
conduct, they can be the nicest, most generous person in the world one
moment, and the next, stab you  in the back and steal everything you own.
Persons playing diabolic characters should take care to recognize the fine
line between roleplaying a cruel, heartless killer and acting to the 
detriment of the mud (i.e., newbie killing, spamming, etc.).

See also: alignments