Traditionally, ruesi are ascetics who live in secluded places outside of society. They engage themselves in mystical forms of practice (such as the making magic potions and all sorts of healing medicines) which derive from the Indian Hindu type of individual ascetic, also known (in Sanskrit) as ṛṣi or yogi. As such, the ruesis stand in stark contrast with the Buddhist bhikkhus, who live in a monastic community and abide the monastic code of discipline (Pāḷi:vinaya).
In Thailand, the earliest sources mentioning the ruesis date from 14th and 15th century legends and myths in chronics (Thai: dtamnaan); therefore, the historiography of the ruesis can be placed somewhere around the early stages of the Ayutthaya period (1351–1767) in Northern Thailand.
Although originally ruesis do not belong to the Buddhist religion (in India), they became, nonetheless, inseparably connected with the form of Buddhism in Thailand, where people worship the ruesis for their attainments of supernatural powers (Pāḷi: abhiññā; Thai: apinihaan). These supernatural powers include several kinds of magical powers, such as:
– levitation, bilocation, walking on water and through walls (Pāḷi: iddhividhā);
– being able to hear conversations of humans, gods, and animals from a far distance (Pāḷi: dibbasota);
– mind reading and teleportation (Pāḷi: cetopariyañāṇa);
– remembering past lives and forms of existence (Pāḷi: pubbenivāsānussati).