The concept of 'evil' does not exist in Hinduism, Buddhism or Jainism. There is no Hindu, Buddhist or Jain equivalent of Satan. Ravana, the Rakshasa-king, is the villain of the epic 'Ramayana', yet he is described as a brahmin, a scholar, a poet and a devotee of Shiva. Bali, the Asura-king, enemy of Indra, is remembered as the harbinger of prosperity. Prahalada, another Asura-king, is a devotee of Lord Vishnu.
So, who exactly are the 'demons' one constantly hears about in sacred stories?
The primal sage Vaishrava, son of Brahma, married two women. One of them gave birth to the race of Yakshas and the other gave birth to the race of Rakshasas. Both were forest sprits: the Yakshas were friendly, the Rakshasas hostile.
The Yakshas knew the secrets of the forests; they knew where rich treasures lay buried. Their leader Kubera built a golden city called Lanka in the middle of the sea. The Rakshasas, led by Ravana, attacked this city, defeated Kubera, drove out the Yakshas and took control of Lanka.
The Rakshasas ruled the forests and hated sages and seers who sought to bring the order of civilization into their realm. They would attack rishis who established ashramas in the forest and tried to perform yagna in the forest. Tired of being persecuted by the Rakshasas, the sage Vishwamitra, sought the help of Dasharatha, king of Ayodhya, who sent his son Prince Rama to defend the sages. Rama killed the Rakshasas and was praised by the sages.
Later, Ravana abducted Rama's beautiful wife Sita. In a great war, with the help of monkeys and bears of the forest, Rama defeated the Rakshasas, killed Ravana and brought peace to the forests.
Also
known as vetala, they are ghosts, goblins and vampires that haunt cemeteries
and ruins. They are hostile spirits of the dead whose children did not perform
funerary rites in their memory. As a result they are trapped in the twilight
zone between life and after-life. They make their displeasure known by troubling
humans. They can drive people mad, kill children and cause miscarriage.
These creatures can be appeased with gifts or frightened them away with spells. One can free them from their ghostly existence by performing their funerary rites.
Being spirits, unfettered by the laws of Space and Time, they have an uncanny knowledge about the past, present and future and a deep insight into human nature. Hence, many sorcerers seek to capture them and turn them into slaves.
A sorcerer once asked King Vikramaditya to capture a vetala who lived in a tree that stood in the middle of a crematorium. The only way to do that was by keeping silent. However, every time Vikramaditya caught the ghost, the ghost would enchant the king with a story that would end with a question. No matter how hard he tried, Vikramaditya would not be able to resist answering the question. This would enable the vetala to escape and return to his tree. The stories of the vetala have been compiled in the book : "Vetala-pachisi".