In Hinduism, a Brahmarshi (Sanskritbrahmarṣi, a tatpurusha compound of brahma and ṛṣi) is a member of the highest class of Rishis ("seers" or "sages"), especially those credited with the composition of the hymns collected in the Rigveda. A Brahmarshi is a sage who has understood the meaning of Brahman or has attained the highest divine knowledge Brahmajnana.
All the hymns of third mandala of the Rig Veda is ascribed to Vishwamitra who is mentioned as son of Gathi, including the Gayatri mantra. According to Puranic stories,Vishwamitra was the only brahmarishi who rose to the position out of pure tapas. Originally belonging to the kshatriya caste of kings and warriors, he rose by pure merit to a Brahmarishi. Vishwamitra is also referred to as Kaushika, because he attained Brahmajnana on the banks of the river Koshi.