Harihara is the fused representation of Vishnu (Hari) and Shiva (Hara) from the Hindu tradition. Also known as Shankaranarayana ("Shankara" is Shiva, and "Narayana" is Vishnu), Harihara is thus revered by both Vaishnavites and Shaivites as a form of the Supreme God.
Harihara is also sometimes used as a philosophical term to denote the unity of Vishnu and Shiva as different aspects of the same Ultimate Reality called Brahman. This concept of equivalence of various gods as one principle and "oneness of all existence" is discussed as Harihara in the texts of Advaita Vedanta school of Hindu philosophy.
Some of the earliest sculptures of Harihara, with one half of the image as Shiva and other half as Vishnu, are found in the surviving cave temples of India, such as in the cave 1 and cave 3 of the 6th-century Badami cave temples.
Vishnu ( holding Sudarshana Chakra) and Shiva (lighter coloured half, wearing tiger skin, holding Trishula) combined in a single Harihara murti, sometimes referred to as Sivakesavaand "Haryadhamurti". The diversity within Hinduism encourages a wide variety of beliefs and traditions, of which two important and large traditions are associated with Vishnu and Shiva. Some schools focus on Vishnu (including his associated avatars such as Rama and Krishna) as the Supreme God, and others on Shiva (including his different avatars such as Mahadeva and Pashupata). The Puranas and various Hindu traditions treat both Shiva and Vishnu as being different aspects of the one Brahman. Harihara is a symbolic representation of this idea. A similar idea, called Ardhanarishvara or Naranari, fuses masculine and feminine deities as one and equivalent representation in Hinduism.
Depending on which scriptures (and translations) are quoted, evidence is available to support each of the different arguments. In most cases, even if one personality is taken as being superior over the other, much respect is still offered to both Vishnu and Shiva by the other's worshippers (i.e. Shiva is still regarded as being above the level of an ordinary jiva and 'the greatest of the Vaishnavas' by Vaishnavas who worship only Vishnu).