Prsnigarbha is the Avatar of Vishnu. He appeared before Dhruva and created the planet known as Dhruvaloka for the habitation of Dhruva.
Birth
Prajapati Sutapa and his wife Prsni worshipped Vishnu with such devotion that He Himself appeared before them for granting boon. In their over enthusiasm they asked thrice "We need a son equivalent to you". Vishnu told them that He Himself will be born as their son in three different janmas (birth). He instructed the importance of brahmacharya to the world.
In the first janma in Satya Yuga, Vishnu was born as Prsnigarba, son of Sutapa and Prsni. In the second life, during Treta Yuga, He was born as Vamana, son of Aditi and Kasyapa. In the third life, towards the end of Dwapara Yuga, He was born as Krishna, son of Vasudeva and Devaki.