Some personalities have such impact that their effect is seen thousands of years after their lifetime.
Yajnavalkya is one such immense personality, a rishi from ancient India who lived somewhere between 800 to 700 BCE. He thus preceded the Buddha by around 300 years.
Although not much is known of his life, his impact is seen more from his works.
He is responsible for several texts and many of the Vedic portions of the Shukla Yajurveda were revealed to him. He is credited with being one of the earliest expounders of Advaita Vedanta.
He is said to have authored many texts, including the Isha Upanishad, the Brihadaranyaka Upanishad, the Yajnavalkya Smriti, Shatapata Brahmana among others.