Sudarshana is a weapon that Vishnu uses for protection, and it is part of many of his incarnations. Vishnu is one part of the Hindu trinity:
1. Brahma (creator)
2. Vishnu (sustainer)
3. Shiva (destroyer).
Vishnu is an Avatar (God who incarnates (comes down) to Earth with a form)) and he had 10 forms:
1. Matsya: He is a fish with a human head. In his hands he holds the Sudarshana Chakra and the conch, which are the two main weapons that Vishnu uses. FISH
2. Kurma: He is a turtle. The Devas (Gods and Goddesses ) had lost strength because of curse madew by a sage so Vishnu incarnated to help regain the kingdom. They had to work with their enemies, who at the time were the Asuras (power seeking dieties, sometimes seen as demons in modern Hinduism). They worked together to access the nectar of immortality so that the Devas could regain the kingdom. To do this they use a serpent as s rope and Mount Mandara as a staff to churn the Earth. In this process many objects come out, including poison which Vishnu drinks. His consort Paravati does not allow him to swallow it, and this is how Vishnu turns blue! Fourteen precious things come from this ending with Dhavantri, the Celestial physician. The Asuras get the nectar of immortality but Vishnu appears again, this time as a beautiful woman, tricks the Asuras and gives the nectar to the Devas who in turn regain the Kingdom. TURTLE
3. Varaha: He is a boar that appeared to rescue Bhu Devi (the Earth) from the Hiraynaksha demon who had stolen her. BOAR
4. Narasimha: Half man, half lion
5. Vamana: In the Bhagavat Purana Lord Vishun incarnates as the Dwarf Vamana to teach the king Mahabali a lesson. The King had become very arrogant and thought that he could give anything to anyone. So Vamana went to him and asked him for land in the size equivlent to three paces. The King granted him this at which time Vamana revealed his identity and took a pace for each of the three realms. This is to teach us to abandon pride and to value wealth as it can easily be taken away. King MahaBali lost his Kingdom and is allowed to revisit once a year. This day is a big celebration in India and is called Onam. DWARF
6. Parasurama: (Ax wielding Rama) The Kshatriya rulers had strayed from the path of Dharma (righteousness) and Vishnu incarnated as Parasurama. He waged war on the entire Kshatriya class for 21 years until he one the Kingdom back. This teaches us faith as 21 years is a long time. It teaches us that destruction and letting go are necessary.
7. Rama: He is the main character of the epic the Ramayana. Rama is the prince of Ayodha and abandons his throne to preserve the honor of his Father. He is exiled into the forest for 14 years. He is joined by his wife Sita and his brother Lakshmana. Many adventures happen during this time, which is a journey of upholding Dharma or righteousness.
8. Krishna: Krishna gives guidance to Arjuna in the Bhagavad Gita.
9. Balarama: ‘Strong Rama” Brother of Krishna.
10. Kalki: The incarnation of Vishnu yet to come.
So Vishnu had many forms that he used to incarnate. In each story, Vishnu is very protective. In order to protect and serve, he uses his conch and his spinning disk which is known as Sudarshana. When we chant Sudarshana mantras, we are calling on this protection.