That which makes it difficult to recognise the presence of real nature of somebody or something

One word substitute is Camouflage.

Cover: put something on top of or in front of (something) in order to protect or conceal it.
Mask: a covering for all or part of the face, worn as a disguise, or to amuse or frighten others.
Pretence: an attempt to make something that is not the case appear true.
Camouflage: hide or disguise the presence of (a person, animal, or object) by means of camouflage.