Brahmarishi in Hinduism is a title for a sage or yogi who attains realization of the supreme Vedic knowledge. The word Brahmarishi has two parts – Brahma (the supreme universal) and Rishi (sage). Thus, Brahmarishi refers to the seeker who has visualized the supreme and contributed to advancing the path of Yoga and Vedic understanding.
The term Brahmarishi is the highest saintly rank achievable, as revealed by the famous tussle between Vishwamitra and Vasishta. The former was called Rajarishi (a royal saint) but he wanted to be recognized as Brahmarishi. Vasishta refused to call him by this title infuriating, Vishwamitra. When Vishwamitra had purged himself of this fury, which was the rajasa (royal) part of him, Vasishta finally called him Brahmarishi.
Hindu Blog On Brahmarishi
A Rishi has all the knowledge but has not freed completely from ego. I am the body concept still lingers in his mind. A rishi has also not freed from the senses. So he can be easily trapped through lust and anger.
A Brahmarishi might walk on earth but has nothing to do with the body. There is no ego as the Brahmarishi has no knowledge of the second. The person is completely merged in the Supreme source. A Brahmarishi has broken the wall of the senses and therefore the person cannot be trapped by anger and lust.