In the Paurava race, there was a king by name Uparichara. He was also known by the name Vasu. He was a virtuous ruler but had a passion for hunting. He conquered the kingdom of Chedi as per the wishes of Indra, the god of the Devas (the celestials). After ruling for many years, Vasu decided to live an austere and peaceful life. He retreated to a secluded place and began to do penance.
Since some kings practicing penance in the past had aimed to become the King of the Devas, Indra became apprehensive of the intentions of Vasu approached him along with some other Gods and persuaded him to resume his duties as the king. They pointed out that his people were looking up to him for protection. They praised his rule pointing out how various sections of people and even animals were happy under his rule, how the economy of his country flourished making the people prosperous and happy. Good governance made life good for people and good life, in turn, promoted virtues and values among people. Families were united with no demand for partition from any member of the family.
Persuaded by the celestials, Vasu returned to his capital to resume his monarchy. Indra who was relieved the he was able to ward off a potential threat to his position as the head of the gods presented Vasu with a crystal car (chariot) that would move in space defying gravity. Only the gods had possession of such a car. He also presented him with a garland of lotuses that would never wilt and remain ever fresh. That garland, known in the earth as Indra's garland, would protect the person wearing it from sustaining injuries in the battle field. Indra also gave him a bamboo pole as a symbolic weapon for protecting the virtuous and punishing the wicked.
One year after receiving the pole, Vasu planted it in the ground, adorned it with clothes and flowers and worshipped it treating it as Indra itself. Indra came to the scene assuming the form of a swan to accept the worship offered. Indra blessed Vasu and and also told him that all kings who would worship him in the form of a pole would receive his blessings. From that time onwards, it has become a practice for all kings on earth to plant a pole in the ground and worship it treating it as a manifestation of Indra.