Brahmarshi[?]Viswamitra is one of the seven venerated sages of Hinduism. He is a kshatriya by birth, but has transcended into the brahmin priestly caste with his tough penance.
Viswamitra has created his own version of Swarga, called Trisanku Swarga, as one of his refugees is repudiated a place in it.
Kousika is one of many gotras[?] that consider Viswamitra as their root node.