Complex sentence: Janaka was not only a brave king but was as well-versed in the shastras and Vedas as any rishi and was the beloved pupil of Yaajnavalkya whose exposition of Brahman to him forms one chapter of the Brihadaranyaka Upanishad.
Split into simpler sentences: Janaka was not only a brave king, but was also as well-versed in the shastras and Vedas as any rishi. He was the beloved pupil of Yaajnavalkya, whose exposition of Brahman to the king forms one chapter of the Brihadaranyaka Upanishad.