The best-known forest-dweller was the sage Yajñavalkya, whose epoch-making explanation of the Self, the absolute cornerstone of all Indian thought, w… - Yajnavalkya

Now as a man is like this or like that, according as he acts and according as he behaves, so will he be; a man of good acts will become good, a man of bad acts, bad;he becomes pure by pure deeds, bad by bad deeds;
And here they say that a person consists of desires, and as is his desire, so is his will; and as is his will, so is his deed; and whatever deed he does, that he will reap.

Similarly, among the stages of life (Ashramas) there were originally only three: as pupil devoted to knowledge, as householder and pillar of society, and as an elderly man withdrawing into the forest, literally or figuratively. The best-known example of the latter stage is when the Seer Yajnavalkya ends his married life and launches the all-important doctrine of the Self in a farewell speech to his wife Maitreyi.

Later, the doctrine of the Self was explicitated by seers like Yajnavalkya, who is up there with Plato as an ideas man next to whom a whole philosophical tradition is but a series of footnotes.