There are two great classifications of such forms of evil and demon spirits in Hindu mythology; one is created by the Gods during the creation of the world and thus brought into the world as demons or Gunas, soon after. The forms of evils and demon spirits in Hindu mythology depend on the cause and kind of death occurred to the individual.
The demons usually act at the orders of the greater deities as Nandi of Lord Siva or the demons, who were decreed by Siva to destroy the yajna by Daksheye Prajapati. The second category comprises of those demons, whose were created due to man, rather to the spirits of men, who have once lived on the earth. The existence of these demons is derived from deceased spirits of dead human beings and it is to these that admiration and propitiation are commonly offered. All malignant devils are believed to have been originally human beings.
If a man is injured and finally killed by a tiger or dies due to snakebite and does not receive proper funeral ceremonies, becomes a ghostly spirit. It is believed that to become an unquiet spirit, roaming about with malicious intentions is only possible if the death has occurred due to sudden and unhealthy reason.