Jamadagni telling about the Kartyaveerarjuna fault to Parashurama
|Family||Richik Muni (father) Satyaavati (mother) (daughter of King Gaadhi)|
|Children||Vasu, Viswa Vasu, Brihudyanu, Brutwakanwa and Rambhadra (also called Parashurama)|
According to Hindu legends, Jamadagni (or Jamdagni, Sanskrit: जमदग्नि) is one of the Saptarishis (Seven Great Sages Rishi) in the seventh, current Manvantara. He is the father of Parashurama, the sixth incarnation of Vishnu. He was a descendant of the sage Bhrigu, one of the Prajapatis created by Brahma, the God of Creation. Jamadagni had five children with wife Renuka, the youngest of whom was Parashurama, an avatar of Lord Vishnu. Jamadagni was well versed in the scriptures and weaponry without formal instruction.
A descendant of sage Bhrigu, Jamadagni literally meaning consuming fire, was born to sage Richika and Satyavati, daughter of Kshatriya king Gaadhi. Growing up he studied hard and achieved erudition on the Veda. He acquired the science of weapons without any formal instruction. His father, Richika had guided him though. The Aushanasa Dhanurveda which is now lost, is about a conversation between Jamadagni and Ushanas or Shukracharya on the exercises of warfare. He went to King Prasenjit, of solar dynasty or Suryavansha, and asked for his daughter Renuka's hand in marriage. Subsequently, they were married, and the couple had five sons Vasu, Viswa Vasu, Brihudyanu, Brutwakanwa and Bhadrarama, later known as Parshurama.
According to the Mahabharat, Jamadagni once became annoyed with the sun god Surya for making too much heat. The warrior-sage shot several arrows into the sky, terrifying Surya. Surya then appeared before the rishi as a Brahmin and gave him two inventions that helped mankind deal with his heat - sandals and an umbrella. 
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Renuka was a devoted wife and a power of her chastity that was manifest. Such was her chastity, that she used to fetch water from the river in a pot made of unbaked clay every day, held together only by the power of her devotion to Jamadagni.
One day while at the river, a group of Gandharvas passed by in the sky above in a chariot. Filled with desire for only a moment, the unbaked pot that she was carrying dissolved into the river. Afraid to go back to her husband, she waited at the river bank.
Meanwhile, Jamadagni noticed that his wife had not yet returned from the river. Through his yogic powers, he divined all that had taken place and was filled with rage. Jamadagni called his eldest son, told him what had happened and asked him to execute his mother. Horror-stricken, his son refused to perform this deed. He then asked all of his sons, and as they refused, he turned them one by one to stone. Finally only his youngest son, Parashurama, was left. Ever-obedient and righteous, Parashurama beheaded his mother with an axe.
Pleased, Jamadagni offered two boons to Parashurama. Parashurama asked that his mother's head be restored to life and his brothers to be turned from stone back to flesh. Impressed by his son's devotion and affection, Jamadagni granted the boons. His brothers and mother were reformed from stone without having the memory of experiencing death as an additional wish of Parashurama. The purpose of this trial was to demonstrate the dharma ("rightful duty") of a son towards his father.
Jamadagni was later visited by the Haihaya king Kartavirya Arjuna (who was said to have thousand arms/hands), who he served a feast using a divine cow called Kamdhenu. Wanting the Divine Cow "Kamdhenu" for himself, the king offered wealth to Jamadagni which he refused. Then the king forcefully took the Kamdhenu with him asking Jamadagni to take it back if possible, but by the means of war, which Jamadagni was not willing to.
Knowing this fact and enraged, Parashurama killed the king, and retrieved the Kamdhenu by killing all of the army of the king Kartavirya Arjuna by himself alone. Later, three sons of the king killed Jamdagni because he was the father of Parashurama who had killed their father, that felt them the proper revenge of eye-for-an-eye. They first stabbed Jamdagni twenty-one times and then sliced his head.
Again enraged, Parashurama killed all three brothers and retrieved the head of his father for cremation, and ultimately enacted a genocide on the kshatriya caste throughout the world for the next twenty-one generations since his mother beat her chest twenty-one times resembling a low-born in mourning after his father was stabbed by the miscreants.
In the Buddhist Vinaya Pitaka section of the Mahavagga (I.245) the Buddha pays respect to Jamadagni by declaring that the Vedas in their true form were revealed to the original Vedic rishis, including Jamadagni.