Mythomania is a psychological term for a habitual liar. It is a pathological defect causing a chronic behavior that is characterized by habitual lying and is consistent with dishonesty.
Another word for it is pseudologia fantastica. Both are a form of mental illness which causes the liar to seek ever increasing amounts of attention. With many people it is caused by low self-esteem, insecurity, social anxiety, or unresolved childhood abuse. If it is caused by a brain injury or dementia it could be the person could seem charming and even charismatic to cover their psychological pain. In other words they lie to make themselves more important.
Another aspect of this disorder is to lash out verbally or physically at anyone who punctures that aura of invincibility and superiority. They simply lie to make themselves more important and must lie more to cover previous lies.
As a person of this mental defect grows older more examinations are preformed to track its progression. Soon they will live in their own reality and their charisma draws others into their reality and lashing out at others becomes a constant need to keep their own fantasy.
The world knows of someone who has all the above behaviors and is worried about its rapid progression. World leaders know they must buy and curry favor to keep from being the object of his verbal abuse and tariffs. When such a person has one of the world’s most powerful militaries nobody knows what could happen.