The Valmiki Ramayana describes Hanuman as a mahapandita (great scholar), Mahavira (of tremendous valor), a master of Veda-s and Vedanga. He is also described later as Bajrang, one who has a body as strong as lightning. By the 10th century Hanuman was regarded as an amsa of Shiva and this association is reflected in many popular prayers to Hanuman like the Hanuman Chalisa. In Maharastra Sri Ramdas, Guru of Shivaji, composed many beautiful stotras to Hanuman of which the Bhimarupi Maharudra is particularly popular.
The strength of Hanuman has always been awe inspiring, and often invoked for protection from any kind of evil, while his Dasabhava, servility to Sri Rama, is a fine example of how the human soul must submit to the power of the Supreme thus transforming itself from a limited animal, a monkey, to the supremely powerful Hanuman.
Photo is a medieval yantra of Hanuman with the Bhimarupi Maruti Stotra inscribed in it. Probably this was used for protective purposes.