Satan or evil is our own Ego out of control. Whenever we become selfish, envious, angry, proud, gritty or hateful, that is evil.
“Evil is only the absence of good, just as darkness is the absence of light.”
“The reality underlying this question is that the evil spirit, Satan or whatever is interpreted as evil, refers to the lower nature in man. This baser nature is symbolized in various ways… If you should leave a man uneducated and barbarous in the wilds of Africa, would there be any doubt about his remaining ignorant? God has never created an evil spirit; all such ideas and nomenclature are symbols expressing the mere human or earthly nature of man. It is an essential condition of the soil of earth that thorns, weeds and fruitless trees may grow from it. Relatively speaking, this is evil; it is simply the lower state and baser product of nature.
It is evident, therefore, that man is in need of divine education and inspiration, that the spirit and bounties of God are essential to his development.” Baha’i Faith
“Things can be evil in relation to one another but not evil in themselves:
“Nevertheless a doubt occurs to the mind – that is, scorpions and serpents are poisonous. Are they good or evil, for they are existing beings? Yes a scorpion is evil in relation to man; a serpent is evil in relation to man; but in relation to themselves they are not evil, for their poison is their weapon, and by their sting they defend themselves… it is possible that one thing in relation to another may be evil, and at the same time within the limits of its proper being it may not be evil. Then it is proved that there is no evil in existence; all that God created He created good. This evil is nothingness; so death is the absence of life. When man no longer receives life, he dies. Darkness is the absence of light: When there is no light, there is darkness. Light is an existing thing, but darkness is nonexistent. Wealth is an existing thing, but poverty is non existing.”
“Satan” – ancient roman word for “animal nature of man”.