Matus is described as a Yaqui Indian to whom Castaneda was first introduced at a bus depot in Yuma, Arizona in the early 1960s. He turns out to be a 'Man of Knowledge' who imparts much of his wisdom and clarity through his 'connection' with Castaneda. The Knowledge is passed on to Castaneda by means of actual experiences, simple exercises and much patience on the part of both which ends in further transforming both characters' view of the world.

Castenada has Juan tell Carlos (the personage representing Castaneda) that he is a brujo (Spanish for sorcerer or medicine man ); a sort of healer , sorcerer or shaman, who had inherited (presumably through a lineage of teachers) an ancient Mesoamerican practice for vastly enhancing one's awareness of, and interaction with, the energies of the Earth and its assorted beings.

In the books don Juan was an expert in the cultivation and use of various psychotropic plants (specifically, psychedelic mushrooms, datura and peyote ) found in the Mexican deserts. These were used as aids to reach states of non-ordinary reality in the teachings he conveyed to Carlos.

In the books the character of don Juan is presented as an unmarried old man, of Yaqui indigenous ancestry, with great strength and agility, who spoke excellent Spanish but had never been to college, and who apparently had lived his entire life in poor conditions. Don Juan's philosophy might be summed up in a passage from Castaneda's first book, The Teachings of Don Juan: A Yaqui Way of Knowledge :