Both Jiva Goswami in his Bhagavata Sandarbha and Krishnadasa Kaviraja in his Chaitanya-caritamrta look to Sripad Vishnuswami for inspiration to establish the essential difference between God and the individual souls and quote from his Sarvajnasukta, his commentary on Vedanta.
Vishnuswami is the founder-acharya of the Rudra sampradaya and is the oldest of the four recognized sampradayas. It is even said that Vishnuswami was born in the Dravida country after the completion of the sacrifice of Janamejaya around the beginnining of Kali-yuga.
Although most scholars are only able to find scanty and conflicting information on Sripada Vishnuswami, Srila Bhaktisiddhanta Sarasvati Thakura gives us an authoritative biographical account of Vishnuswami which we accept to be accurate.
There were three Acharyas bearing the name of Vishnuswami in the Rudra sampradaya. The first is called Adi Vishnuswami who is said to have been born about the third century B.C. in the Pandyan country. Vishnuswami's father Devesvara was the royal priest and minister. Devatanu, as he was known before he took the sannyasa name of Vishnuswami, was trained by his father in a vigorous theistic education, to fight Buddhism. The Pandyan king exerted all his influence to crush Buddhism in particular and other non-va isnava sects in general. King Pandyovijaya and his minister, Devesvara, went to Puri and recovered the Deities of Jagannatha, Balarama and Subhadra, which had been turned into the Buddhist Dharma by Buddha and Samgha by the Buddhists. King Padyovijaya and Devesvara removed the deities from the main temple to sundaracala about two miles away by cart. This is said to be the origin of the Rathayatra of Jagannatha. Now the ceremony of conveying the Deities from the temple to the car is named Pahandi or Panduv ijaya. The word Panda is applied to the priests of Jagannatha and is said to be derived from the "Pandya". The Deities were again brought back to the temple after Buddhism had been supressed to some extent.
Vishnuswami was the first to adopt tridandi sannyasa which he brought into practice among his seven hundred sannyasa disciples. It was he who introduce the Astottara satanami sannyasa (108 designations of sannyasis) including the dasanami which was adopted by sankara in his sect. It was not sankara who originated it as some scholars think. Vyasesvara was the last in the line of Sannyasis, after whom the line became almost extinct, until it was revived by Raja Gopal who also assumed the name of Vishnuswami in the beginning of the 9th century. His main follower was Bilvamangala.
Raja Gopala Vishnuswami revived the old Vishnuswami line and began the active propaganda with renewed vigour and enthusiasm. He installed the Varadaraja temple in Kanci, Ranchorlal in Dwaraka and many other Deities in different places of pilgrimage. He converted many of Sankara's prominant disciples after Sankara's death.
After the disappearance of the second Vishnuswami a great feud took place between his community and that of Saiva sivaswami who regards Rudra as an independant God while the former holds Rudra as Guru and the intimate associate of Vishnu. The Saiva opposed it vigorously and people failing to appreciate the subtle point of theism in the Suddhadvaita system of Vishnuswami, became inclined to Saivite monism, which soon became embraced by the population in general. The Saivaite community taking advantage of the situation, tried to misappropriate Vishnuswami's Sarvajnasukta and modified it to a great extent to suit their system.
The third revival came under Andhra Vishnuswami in the 13th century whose successors included Laksmana Bhatta, the father of Vallabhacharya. This Vishnuswami is said to have been the son of a minister of a Dravidian prince under the Emperor of Delhi.
Vishnuswami's philosophy is visuddhadvaita. Brahman as Vishnu, Narasimha, non-dual and having no second. Brahman has all contradictory qualities. The soul is part of Brahman like spiritual sparks, real, eternal, atomic and dependent. Creation has no motive, it is like a cosmic game and it directly emanates from Brahman. The cause of bondage is one's attachement to karma. The process of release is devotion based on Bhagavata. The goal of life is to attain uninterupted contact with Krishna, Vaikuntha salokya where there is no return.
Text from: India Divine
The fourth Vaishnava acharya, Vishnusvami, representative of the Rudra sampradaya (who worship the avatara of God known as Narasimhadeva) is less known than the other three.
Actually there is some confusion about him, as it seems there have been three Vishnu Svamis: Adi Vishnu Svami (around 3rd century BCE, who introduced the traditional 108 categories of sannyasa), Raja Gopala Vishnu Svami (8th or 9th century CE), and Andhra Vishnu Svami (14th century).
The emphasis of this school, called suddha-advaita ("pure monism"), is on the concept of lila or the pastimes by which God can be transcendental and immanent according to His will. Thus everything is pure, including the material universe, that is created by God and intimately related to Him. In his method of worship, Vishnusvami gives preeminence to Rama, the previous avatara before Krishna.
Vishnusvami visited Puri and founded there the Jagannatha Vallabha Math in the gardens of the temple, where Ramananda Raya also established his spiritual school.
Among the famous followers of this sampradaya we can mention Sridhara Svami (who became famous for his commentary on the Bhagavata purana).
Text from: Stephen Knapp