It is believed that lord Surya himself placed this form, khakholkh Aditya, which is now situated in the kameshwar temple.
Khakholkh Aditya as a form of Surya dev has a history behind its name. Sage Kashyap was one of the Saptarishis, the seven ancient sages of the Rigveda. although he had many wives of which Vinata and Kadru were sisters and gave birth to 2 different species. Vinata gave birth to Garud where as Kadru gave birth to snakes.
Being sisters, they both were very different from each other. Kadru was very clever and devious, whereas Vinata was peaceful and innocent.
One day Kadru asked Vinata to play a game in which she challenged Vinata to guess the color of the Uchchaihshravas, said to be Indra dev’s vahana [vehicle]. Vinata knew and gave the right answer with “white”. but Kadru cleverly tricked her. she told her son to twin around the tail of Uchchaihshravas so that it will look greyish black, the same as the snakes.
As per the rules, Vinata held to give the wrong answer and had to serve Kadru and her sons by becoming their slaves. Garuda used to watch her mother being treated as a slave by Kadru and her son. he could not hold up more and decided to free his mother.
One day he asked Kadru and her son to release his mother by freeing her. they agreed but on a condition, they asked Garuda to bring Amrit. Garuda accepted the condition, but the task was not that simple.
Amrit, the heavenly nectar of immortality emerged from the churning of the ocean of milk. it is guarded by devas. he has to chase devas to get to the Amrit. he defeated Indra and other devas and quickly took the pot of Amrit, and went back to the kadrus palace, this selfless act of garuda impressed Lord Visnu.
Later Lord Vishnu offered Garuda to be his vehicle, Garuda accepted the offer. Lord Vishnu told garuda to protect Amrit from snakes and not allow them to drink it. Garuda quickly went back to Kadru’s palace and gave Amrit to them.
They released Vinata and took Amrit from Garuda to drink it. Garuda stopped snakes and Kadru to prevent Amrit and told them to clean themselves first. they agreed and went to take bath.
In the meantime, Lord Vishnu appeared to take Amrit back, as per the rule, snakes were not allowed to have Amrit. as soon as they were back they saw nothing but a few drops of Amrit laying on the grass, and they quickly started licking the grass to have as much as they can. The sharp blade of the grass split their tongues. From that day, snakes started having split tongues. it is also believed that they consumed Amrit which was not rightfully earned.
After that Vinata urged Garuda to take her to Kashi so that she can repent for her sins. Garuda took her to Kashi where Garuda installed a Shiv Ling, which is popularly known as the ‘Garudeshwar temple’. Vinata started worshipping Lord Surya in his form as Khakholkh Aditya. Lord Shiva appeared in person and blessed Garuda stating that the latter would be known by everyone in the world as the vehicle (vahana) of Lord Vishnu. [as per Kashi Khand, Chapter 50]
As per a popular belief, who ever pray to Surya dev in a form of Khakholkh aditya gets rid of all sins.