Does the concept of Evil Spirits occur in Hinduism?
There's no equivalent of Satan in Hinduism. Hinduism has a universal Brahman which pervades all things good as well as evil. Satan (an absolute evil) is a necessity in Abrahamic faith to explain all things bad because the Abrahamic God cannot do anything evil. Hindu God on the other hand pervades everything good as well as bad.
According to the Vedas, there are only three principles or entities that exist in reality, in sum total. These three are: Brahm (God), Jeevatma (the countless souls) and Maya (the material energy). Indeed, the universe is made up of these three entities alone. There never was a fourth being and there never will be a fourth being.
All the 'demons' in the Hindu religion are classified under the 'soul' category. Due to their Karmas (actions) they are born in those wicked races and have such sinful propensities. The Upanishads state that no one can be equal to God ("Eka mevadveeteeyam brahm"). He is unmatched in power, stature or opulence. Thus, there is no room for any independent being to work against the will/design of God in Hinduism.
Besides, Hindu scriptures state that any person performs actions only according to his will. Of course, these actions are shaped by his company and atmosphere, but there never is any inherently evil being whispering sin into his ears.
In fact, Hinduism denies the very idea of evil. Evil, according to the Hindu scriptures, is non-existent. There are three modes of nature - sattva, rajas and tamas. The demons and other cruel people are said to be possessed of tamas, but even they can overcome this darkness by purifying their mind through association with sattvic matter/personalities.
The world consists of the illusory duality of knowledge and ignorance. It contains of knowledge and devotion, and also attachment to 'lust and greed'; righteousness and unrighteousness; good and evil. But Brahman is unattached to these. Good and evil apply to the jiva, the individual soul, as do righteousness and unrighteousness; but Brahman is not at all unaffected by them.
One man may read the Bhagavata by the light of the lamp, and another may commit a forgery by that very light; but that lamp is unaffected. The sun sheds its light on the wicked as well as on the virtous. You may then ask, 'How, then can one explain misery, and sin and unhappiness?' The answer is that these apply to the jiva. Brahman is unaffected by them. There is poison in a snake; but though others may die if bitten by it, the snake itself is not affected by the poison.
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