Santhal religion, the supreme deity, who ultimately controls the entire universe, is Thakurji

Santhal

According to the Santhal religion, the supreme deity, who ultimately
controls the entire universe, is Thakurji. The weight of belief,
however, falls on a court of spirits (bonga ), who handle different
aspects of the world and who must be placated with prayers and
offerings in order to ward off evil influences. These spirits operate
at the village, household, ancestor, and subclan level, along with
evil spirits that cause disease, and can inhabit village boundaries,
mountains, water, tigers, and the forest. A characteristic feature of
the Sanhthal village is a sacred grove on the edge of the settlement
where many spirits live and where a series of annual festivals take
place.[1]

The most important spirit is Maran Buru (Great Mountain), who is
invoked whenever offerings are made and who instructed the first
Santals in sex and brewing of rice beer. Maran Buru's consort is the
benevolent Jaher Era (Lady of the Grove).

A yearly round of rituals connected with the agricultural cycle, along
with life-cycle rituals for birth, marriage and burial at death,
involves petitions to the spirits and offerings that include the
sacrifice of animals, usually birds. Religious leaders are male
specialists in medical cures who practice divination and witchcraft.
Similar beliefs are common among other tribes of northeast and central
India such as the Kharia, Munda, and Oraon.[1]

Smaller and more isolated tribes often demonstrate less articulated
classification systems of the spiritual hierarchy, described as
animism or a generalized worship of spiritual energies connected with
locations, activities, and social groups. Religious concepts are
intricately entwined with ideas about nature and interaction with
local ecological systems. As in Santal religion, religious specialists
are drawn from the village or family and serve a wide range of
spiritual functions that focus on placating potentially dangerous
spirits and coordinating rituals.

Others

Unlike the Santhal, who have a large population long accustomed to
agriculture and a distinguished history of resistance to outsiders,
many smaller tribal groups are quite sensitive to ecological
degradation caused by modernization, and their unique religious
beliefs are under constant threat. Even among the Santal, there are
300,000 Christians who are alienated from traditional festivals,
although even among converts the belief in the spirits remains strong.
Among the Munda and Oraon in Bihar, about 25 percent of the population
are Christians. Among the Kharia of Bihar (population about 130,000),
about 60 percent are Christians, but all are heavily influenced by
Hindu concepts of major deities and the annual Hindu cycle of
festivals. Tribal groups in the Himalayas were similarly affected by
both Hinduism and Buddhism in the late twentieth century. Even the
small hunting-and-gathering groups in the union territory of Andaman
and Nicobar Islands have been under severe pressure because of
immigration to this area and the resulting reduction of their hunting
area.[1]

Pressure to convert to Major religions

Some of pressure is intentional, as outside missionaries work among
tribal groups to gain converts. Most of the pressure, however, comes
from the process of integration within a national political and
economic system that brings tribes into increasing contact with other
groups and different, prestigious belief systems. In general, those
tribes that remain geographically isolated in desert, hill, and forest
regions or on islands are able to retain their traditional cultures
and religions longer. Those tribes that make the transition away from
hunting and gathering and toward sedentary agriculture, usually as low-
status laborers, find their ancient religious forms in decay and their
place filled by practices of Hinduism, Islam, Christianity, or
Buddhism.[1]

Folk Hinduism or Popular Hinduism is the aspect of Hinduism as a folk
religion, i.e. nominal Hinduism mixed with Animist practice, as
opposed to its scholastic or mystical aspects (Brahmanism, Vedanta,
Hindu philosophy). Folk Hinduism is emphatically polytheistic, as
opposed to Brahmanism or Vedantic Hinduism, which emphasize Monism or
Monotheism.