This king is mentioned by Manu as having come into conflict with the Brahmins, and his story is repeated several times with variations in different parts of the Mahabharata as well as in the Puranas. According to Manu "By sacrifices, austere fervour, sacred study, self-restraint, and valour, Nahusha acquired the undisturbed sovereignty of the three worlds. Through want of virtuous humility the great king Nahusha was utterly ruined".
One version of the narrative says that he aspired to the possession of Indrani, wife ofIndra, when that god had concealed himself for having killed a Brahmin, Vritra. A thousand great Rishis bore the palanquin of Nahusha, and on one occasion he touched with his foot the great Agastya, who was carrying him. The sage in his anger cried out, "Fall, thou serpent," and Nahusha fell from his glorious car and became a serpent.
Agastya, at the supplication of Nahusha, put a limit to the curse; and according to one version, the doomed man was released from it by the instrumentality of Yudhishthira, when he threw off "his huge reptile form, became clothed in a celestial body, and ascended to heaven."
Sister Nivedita also has mentioned about the king Nahusa in one story "The Worth of Kine" in relation to rishi Chyavana who was accidentally caught in a net along with fish by fishermen who were fishing in a river. The fishermen took the rishi Chyavana to king Nahusha and asked him to pay the price for the fish and the rishi, with the king offering a cow in return for the sage.
BIRTH:-
King Aayu's wife's name was Indumathi. Both were very happy to have a son. But the same night a maid lifted the sleeping child and took him in the sky. in fact she was not a maid, she was the Asura Hund. Hund brought him to his palace and handed over to his wife to cook a delicious dish for him. The cook could not kill the child and she gave him to a man who took him away and left him on the doorstep of Sage Vasishta. It was morning and Sage Vasishta was going for his morning chores that he saw a newborn child on his doorstep, he picked him in his arms and named him Nahusha. On the other side Aayu and his wife were crying for their child, that Narada arrived and consoled them that their child was safe.
NAHUSHA and Rishi CHYAVANA:-
According to one version, he became Indra (king of devas :residing in Indralokam) at one time. He lusted after the current Indrani, Sachi(queen of the devas who was the previous Indra's wife). He sent a message to Indrani that since he had become now Indra he was coming to her palace. Indrani got worried but couldn't do anything. So she went to the Guru of the Devas, Brihaspathi and told him her problem. He suggested that she should ask him to come in a palanquin carried by Sages and she laid the condition to Nahusha. In his arrogance Nahusha didn't realize the impropriety in asking Sages to be his bearers.
The Sages were not used to this work they were moving slowly and in particular Sage Agastya, who was short in stature. Nahusha was in hurry to meet Indrani, so he kept shouting "sarpa sarpa" (Sanskrit word with multiple meanings one of which was "go fast" ). At one point he goaded Agastya with his foot and said "kumbhadimba sarpa sarpa"(kumbhadimba means one born of a pot - Agastya was said to have been born out of a pot). The enraged Agastya retaliated by a curse "sarpo bhava"(become a snake). The King Nahusha turned into a snake fell down to Earth. Sage Narada intervened on his behalf and Agastya relented and said that Yudhishthira would be instrumental in Nahusha's release from the curse.
SECOND STORY from PADMA PURANA
Credit:- http://hindumythologyforgennext.blogspot.in/2012/06/birth-of-nahusha-part-3-of-3.html
Sage Vashishta looked at surprise as he saw a beautiful baby peacefully sleepig just outside his ashram. He picked up the baby & looked around & saw that nobody was around there near the baby.
Puzzled Sage Vashishta looked at the child once again.The child had precious ornaments...This is a royal child..Now why would anyone leave their prince at my door step.Sage Vashishta closed his eyes & meditated.Using the piwers of his mind 'saw' what happened to this child..The child had been kidnapped by Hund.. Hund cook had saved the child. Sage Vashishta opened his eyes & looked at the child who had now opened his eyes & looking at the sage.
Sage Vashishta picked up the baby in his arms. The baby snugly fit in his arms as the sage looked at the child once again. His parents had named him Nahusha... Sage Vashishta smiled.. The child was indeed Nahusha, which meant one who not to be frightened...That is when Sage Vashishta had another flash of insight.. He saw Goddess Parvati & Lord Shiva visit Nanadakannan...There Goddess Parvati had wished for a daughter from a Kalpataru tree...As a result of which she had a daughter named Ashosundari... Godess Parvati had blessed Ashoksundari that she would marry Nahusha... Sage Vashishta smiled again.Goddess Parvati had wanted Ashoksundari to marry this Nahusha.
Sage Vashishta then brought up Nahusha as his own son in his ashrama.The boy was a quick learner with a good grasp. Nahusha also learnt how to use weapons. Learning from Vashishta & living in a forest, Nahusha soon became brilliant & brave hunter... But that was not all... Nahusha never understood why the sage also taught him the art of diplomacy & the art of administration of a kingdom...
Soon Nahusha was a fine man... One day Nahusha saw a man come to the hermitage & talk to the sage. Sage Vashishta invited Nahusha to come to the discussions.The man looked tired & thoroughly harrased... Nahusha wondered what was wrong... The man spoke with almost eyes filled with tears, 'Sir ! It is Hunda sir...'The man shuddered as he continued,'This Hunda is a menance... He terrorises all people in the area surrounding the forest... People are afraid to face him.. because he is so strong & powerful.'
Sage Vashishta looked at the man & glanced at Nahusha as he asked 'This Hunda.. Has he always been like this?'
The ma nodded his head, 'For the past many years, he has been troubling everyone... Ever since he kidnapped the prince of Prathishthana ...'
Nahusha felt something deep within himself as he heard the name Prathishthana... It was as if something about this place was calling out to him... Besides the words of the man struck him odd . 'The prince of Prathishthana.'
'Yes Sir !'.The amn looking at him for the first time, 'Sir, you see, King Aayu & Queen Indumathi had a son,Hunda kidnapped the child when he was just a year old... What happened to the prince nobody knows... Most of the people think that the prince is dead... which is very possible..' The man shivered again 'However the king & queen, they are stubborn.They are steadfast in their belief that their son will come back.'The man shook his head his in admiration, 'It is almost as if they are sure that their son is alive...'
Nahusha listened as the man spoke of how Hunda was troubling villagers... Nahusha got angry... This Hunda was menace.. He had to be stopped..
Sage Vashishta spoke, 'Don't worry ! Consider your problem is solved...' Sage Vashishta looked at Nahusha & spoked with quite conviction, 'Hunda will never trouble anymore...' The man looked at sage & nodded his head. he bowed to the sage & left.
Sage Vashishta then turned to Nahusha, 'Nahusha ! Before you set about fulfilling your destiny, there is a story I have to tell you.'
Nahusha listened with surprise as he sat down beside the sage to listen to what sage had to say.Sage Vashishta told a dazzled Nahusha, all about his birth, how he came to the ashrama... Nahusha slowly nodded his head spell-bound. Sage Vashishta gave a wo=uick smile & said 'Well prince of Pratishthana...' Nahusha felt stunned on hearing sage Vashishta address him like this, 'There is another story that you need to know.. that is of .. Ashoksundari'
Nahusha looked puzzled as the sage continued, ', she is the wish born child of Lord Shiva & devi Parvati..' The sage smiled as he continued, 'Goddess Parvati blessed her that she would marry a great king named Nahusha...' Nahusha looked surprised as the sage continued, 'Subsequently Ashoksundari met Hunda...' nahusha was alarmed as the sage continued...', she managed to escape from him... But that day Ashoksundari cursed Hunda, that he ould be killled by her future husband.. Hunda is destined to be killed by you...' the sage continued & looked at Nahusha who looked like a million thoughts were going around his head at the same time...
Finally Nahusha with the blessings of his guru left to kill Hunda
There was a firece battle between Hunda & Nahusha.. Nahusha was taught by Rishi Vashishta & he was a brilliant fighter.. Hunda was struggling to keep up with Nahusha ... Finally after being defeated by Nahusha, Hunda was killed by Nahusha.. Everbody rejoiced at the death of demon.
Nahusha then went to the kngdom Prathishthana. King Ayu & queen Indhumati were thrilled on seeing their son come back to them.. Indumathi rejoiced after seeing her son now a fine man, who was all set to take the mantle of being the king of the kingdom...
There was even more cause to celebrate when Nahusha went & met Ashoksundari. Ashoksundari shyly met Ashoksundari as it was love at first sight,Ashoksundari had heard a lot about nahusha's bravery & waited for him to come once... ever since sage Vashishta had told him about Ashoksundari, Nahusha had learnt everything he could about her.. He heard about her beauty & intelligence & was smitten by her...
The kingdom of Prathishthana celebrated the wedding of their heir- Nahusha & Ashoksundari
Afetr becoming the king of Prathisthana, he ruled the kingdom of Prathisthana well & he even performed a hundred of Ashwamedha Yagnas. He was a good king that the Devas appointed him to be their king, in absence of Devraj Indra.
Nahusha falls from heaven:-