In the Sinhaasan Batteesee, an account of Vikram and Shaalivaahan, the founder of the Shak Era, is given, which in short is as follows : --

Who was Shaalivaahan
Shaalivaahan was a Satavaahan King, sometimes called Gautamee Putra Satakarnee. He is most popularly known as the initiator of Shaalivaahan or Shak Samvat. This day is to celebrate his victory over Shak in the year 78 AD. He was a son of Kumbhaar (potter) that is why sometimes he is called Kumbhaar Raajaa Shaalivaahan. When Satakarnee ascended the throne of his father Satakarnee, he was facing threats from Shak and Yavan etc. He defeated them all and established his Kingdom. He as succeeded by his son Vashishth Putra Shree Pulamaavee in about 130 AD.

There lived a rich merchant in Purandarpur. He had four sons. He gave a sealed earthen pot to each of his four sons before his death, with the instruction that they would not open it before his death. After some time he died. His four sons opened their pots. When the pots were opened, the first pot was found to contain some earth, the second one contained coals, the third one contained bones, and the fourth one contained bran. They could not understand its meaning, so they went to their King Vikram and requested him to explain the meaning of the contents, but he also could not do so. So the sons went to Pratishthaanpur, but there also nobody including its King could solve the problem. A wonderful child, however, succeeded in explaining the same.

The child was the offspring of a Braahman widow, who had lost her husband when she was very young. She had two brothers. She conceived by a Naag Prince, and so her brothers were very ashamed of their sister. They left the country. The unfortunate widow was, in her distress, sheltered by a potter, where she was delivered of a male child, who was called Shaalivaahan by his mother. The child, hearing of the Brahman's riddle, went to the King and answered the problem as follows :

--The first pot which contained the earth entitled the owner to his father's land property; --the second pot contained the coals so the second son was to inherit all the timber and wood belonging to his father;
--the third pot contained the bones so the third son was to get the elephants, horses, cattle, and animals of all kinds belonging to his father; and
--the fourth son who found bran in his pot, got all corn and grain which belonged to his father.

Vikram also heard this. On hearing this, he sent for the child, but he refused to go to Vikram, and said that instead of his going to Vikram, there would be a time when Vikram himself would have to come to him. Vikram was very angry at this bold answer so he decided to kill that boy. With the mind of killing the boy Shaalivaahan, Vikram proceeded to the boy with a large army. The boy was making clay figures of soldiers and animating them. A desperate battle was fought between Vikram's soldiers and the boy's animate soldiers, but the Naag's son (Shaalivaahan), stupefied Vikram's army. Vikram found his soldiers asleep so he requested the assistance of Vaasuki Naag. Vaasuki Naag gave him Amrit with which he could revive his troops. Hearing this, Shaalivaahan sent his two men for some of the Amrit, and Vikram complied with his request.  This legend ends here.

Another Legend
According to another legend, Shaalivaahan was the son of a Braahman girl who was a sojourner at Paithan and lived with her two brothers in the house of a potter. On an occasion she went to the Godaavaree to bathe, Shesh Naag, the king of serpents, becoming enamored of her, transformed himself into a man and embraced her. In due course she gave birth to a boy who was named Shaalivaahan. He was brought up in the house of the potter. After sometime the King Vikramaaditya of Ujjain, to whom a certain deity had revealed that he was destined to die at the hands of the son of a girl of two years, sent about his Vaitaal or king of Ghosts to find out if there was such a child anywhere. The Vaitaal saw Shaalivaahan playing with his girlish mother and informed Vikramaaditya about him. Thereupon he invaded Paithan with a large army, but Shaalivaahan infused life into clay figures of horses, elephants, and men, by means of a charm communicated to him by his father Shesh Naag and encountered Vikramaaditya, and defeated him.

Another Account
Another account states that there was a voice from Heaven which settled the dispute between the rival combatants (Vikramaaditya and Shaalivaahan) by allowing each of them to reign on the two portions of the country separated by the Narmadaa River.

Shaalivaahan has been described as a devout and learned man, who, after a time, renounced the world and passed his remaining days in retirement and meditation. The peculiarities with these two remarkable characters are that a great deal of their life is enveloped in mystery, and several Vikram and Shaalivaahan have from time to time risen to vie with each other as rival combatants.

Both have started Samvat (era) on their names - Vikram Samvat and Shaalivaahan or Shak Samvat. When the Shak Samvat was attributed to him, it is difficult to determine precisely, but all the copper plates up to the 11th century AD speak of "Shak Nrip Kaal", meaning the era of Shak King.