Lord Shiva is the spiritual master of everyone, both the dull and demoniac and the highly learned vaisnavas.

Lord Shiva is described here as caracara-guru, the spiritual master of all animate and inanimate objects. He is sometimes known as Bhutanatha, which means “the worshipable deity of the dull-headed.” Bhuta is also sometimes taken to indicate the ghosts. Lord Shiva takes charge of reforming persons who are ghosts and demons, not to speak of others, who are godly; therefore he is the spiritual master of everyone, both the dull and demoniac and the highly learned Vaisnavas. It is also stated, vaisnavanam yatha sambhuh: Sambhu, Lord Shiva, is the greatest of all Vaisnavas. On one hand he is the worshipable object of the dull demons, and on the other he is the best of all Vaisnavas, or devotees, and he has a sampradaya called the Rudra-sampradaya. Those who do not regularly bathe are supposed to be in association with ghosts and crazy creatures. Lord Shiva appeared to be like that, but his name, Shiva, is actually fitting, for he is very kind to persons who are in the darkness of the mode of ignorance, such as unclean drunkards who do not regularly bathe. Lord Shiva is so kind that he gives shelter to such creatures and gradually elevates them to spiritual consciousness. Although it is very difficult to raise such creatures to spiritual understanding, Lord Shiva takes charge of them, and therefore, as stated in the Vedas, Lord Shiva is all-auspicious. Thus by his association even such fallen souls can be elevated. Sometimes it is seen that great personalities meet with fallen souls, not for any personal interest but for the benefit of those souls. In the creation of the Lord there are different kinds of living creatures. Some of them are in the mode of goodness, some are in the mode of passion, and some are in the mode of ignorance. Lord Vishnu takes charge of persons who are advanced Krishna conscious Vaisnavas, and Lord Brahma takes charge of persons who are very much attached to material activities, but Lord Shiva is so kind that he takes charge of persons who are in gross ignorance and whose behavior is lower than that of the animals. Therefore Lord Shiva is especially called auspicious.

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fourth Canto, Chapter 02 – Text 02 & 15