All religions have their explanation and origin of evil. Christianity, Islam and Zoroastrianism postulate an external element named Satan or Ahriman or Angra Mainyu who is responsible for evil. In these religions, evil is therefore external to one self. While in Christianity and Islam, Satan is a fallen angel, in Zoroastrianism, Ahriman or Angra Mainyu, co-evolved with Time itself. Indic religions have a different view of it. In Dhammapada, Buddha says – “By oneself, indeed, is evil done; by oneself is one defiled. By oneself is evil left undone; by oneself, indeed, is one purified. Purity and impurity depend on oneself. No one purifies another.” (Dhammapada chapter 12, verse 165).
What is the Hindu view of evil? The two eternal contestants in Hindus are Devas (lit: The shining ones) and the Asuras (lit: the ungodly). Chāndogya Upaniṣad, relates the story of Indra (lit: residing within), the king of Gods and Virochana (lit: shining), king of Asuras went to Prajapati (All Father, the Creator) for instruction. When Prajapati instructed Indra and Virochana first saying that this body is Brahman, they both were satisfied. However Indra upon reflection thought instruction was not complete and went back again and again. However, Virochana instructed his Asuras as the body is be all and end all and not caring for anything other than their own bodies. The Upanishad says “Therefore even today they say of one who does not practice charity, who has no faith and who does not perform sacrifices: “He is verily a demon”; for such is the doctrine of the demons. The demons deck the bodies of the dead with garlands and perfume, with raiment and with ornaments, for they think that thus they will win the world beyond.” [For reading the full story in Chāndogya Upanishad (Chapter VIII), please click here]. Rama battles demons who want to destroy the sacrifice of Vishwamitra. Rig Veda is full of stories about Indra battling Panis who hold back wealth and water. The Panis were regarded as niggardly and uncharitable.
What has the mythology got to do with evil you ask? Well just this. Remember Chāndogya Upaniṣad states that the Asuras bedeck their bodies with garlands and perfumes, with raiment and with ornaments for they think with this they will win the world beyond. Basically anyone who has an excessive preoccupation with his own self here and now, materialistic, selfish (uncharitableness is a result of selfishness), headless of the world beyond is an Asura, i.e., the ungodly who are regarded as the source of evil. This excessive preoccupation of self to the exclusion of others and hereafter is the source of all evil in this world.
- Vision and Approaches of Upanishads (slideshare.net)