In Hindu mythology, ten avatars of Lord Vishnu are famous even though he has lot of more incarnations. There is a story behind these incarnations.
Long back once a king was performing some Vratham(Holy Penance). All sages/saints are invited. Vratham was almost over. Last step was to serve food to all sages and finally king has to eat before sunset. Everybody were waiting for sage Dhurvasa to come. Finally he reached. King invited him and offered him to have food. Then sage said that he and his disciples will go to nearest river and wash their hands and come back.
Again all were waiting for Dhurvasa to come back. It was almost sunset and if king didn't eat anything, vratham will be a waste. So some sage among them advised the king to have some water which will complete vratham successfully and as he didn't eat anything, it wont conflict with condition that he should eat after all sages finished eating. So king had some water. Exactly at that moment sage Dhurvasa arrived and got angry.
He started scolding the king furiously. He started cursing him like "You will take a life of fish, tortoise, pig, beast ... so on". That poor king was helpless and just folded his hands to god and meditating. Then Lord Vishnu took over his body and accepted all Dhurvasa's curses. After some time, even god got angry. He left his Sudharshan Chakra on him. Then sage Dhurvasa got scared and started running to save his life. He went to Lord Brahma. He said that he is incapable to defend Sudharshana Chakra. Later he went to Lord Shiva to get the same answer. Finally he went to Lord Vishnu and pleaded for mercy. Then Lord Vishnu told him to ask the king for forgiveness to save his life. Then Dhurvasa had to ask pardon to that king to save himself.
Later Lord Vishnu had to take all his avatars because of curses by sage Dhurvasa. Famous 10 among them are as follows:
2. Kurmavatar
3. Varahavatar
4. Narasimhavatar
5. Vamanavatar
6. Parashuramavatar
7. Ramavatar
8. Krishnavatar
9. Budhavatar
10. Kalki avatar
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