Here is Bhāgavatam’s description of Dhruva’s oldest son (4.13.6~11):
When Dhruva retired finally to the forest, his eldest son Utkala had no interest in the opulence and kingdom granted by the royal throne. From the beginning, Utkala was a detached and desireless person, seeing everything in the world as having the same value, since the Supersoul expands as everything.
He recognized himself as pure spiritual energy, without any wants or needs. The taste of this enlightenment compelled him to cast away all separatism and embrace the continuous bliss of unity. His incessant fire of yoga burned away all traces of his karma. He could then see that the true form of everything was nothing but the soul.
Although he certainly was not retarded, blind, deaf, insane, or stupid, childish people saw him like that. He was like a fire that showed no flame. The family elders and ministers assumed that he was retarded or insane, so they enthroned his younger brother Vatsara, Bhrami’s son.
comments: Everything is divine (“Supersoul expands as everything”), so nothing is better or worse than anything else. To be rich is no better or worse than to be poor. To be pretty is no better or worse than to be ugly. A diamond is no better or worse than a common stone. Knowing this deeply, Utkala had not interest in trying to avoid or attain anything – he was “detached and desireless.”
“He recognized himself as pure spiritual energy” – he recognized that the essence of all things (including himself – ātmānām) was homogenous spiritual energy (brahman) which has no wants or needs (nirvāṇa). This is a delightful thing to recognize, it has rasa — “avabodha-rasa” (it is an experience included in śāntra-rāsa, and therefore in all spiritual rāsa). So, it gave him a “higher taste.” This inspired him to discard the common prejudices based on wants and needs. He embraced unity, absolute equality, and therefore experienced uninterupted bliss (ānandam anusantata).
Still, he practiced sādhana (yoga) to refine this inspiration and make it a complete, perfect realization. Upon attain that he saw it everywhere constantly – “He could then see that the true form of everything was nothing but the soul.” (nātmano’nyaṁ tadaikṣata).
“A fire without flame” – his consciousness (fire/light) was not active externally, therefore the childish people in the external world (bālānām) could not see much light from his consciousness – he seemed deaf, dumb and blind, etc. “retarded” (jaḍa).
Even the ministers and elders of Dhruva’s earthly kingdom seem to have had this opinion. Or, we might insert the idea that they realized that functionally he was as good as a retarded or insane person.
Vraja Kishor dās
The Enquirer 