The teacher, the guru, the expert, the coach, the psychologist, a friend, a sage, a man of wisdom, a guide, a healer, the adviser, spiritual master… You can choose what you like best and what appeals to you personally. Those who work with him call him Master. One of the meanings of the verb "to master" goes for "to know something in perfection, to take the control (over feelings and emotions), to control and rule", as an adjective "master" means "highly qualified".