Kroni (Tamil: குறோணி) is a figure in Ayyavazhi mythology. He is the primordial manifestation of evil, and manifests in various forms of evil, such as Ravana and Duryodhana, in different ages or yugas. In order to counteract and destroy the evil of Kroni's manifestations, Mayon (a Tamil name for Vishnu) incarnates as Avatars such as Rama and Krishna. Kroni is analogous to Satan in the Judaeo-Christian tradition. He shares many similarities with the demon Kali of the Mahabharata and Kalki Purana.
Read more about Kroni: Kroni in The Akilattirattu Ammanai, Fragments of Kroni, Philosophical View