Question: in which yuga lord vishnu was born?
Answer: Vishnu's guardians Jaya-Vijaya, were cursed by 4 kumara sages (Bramha's sons) to incarnate on Earth either 3 times as enemies of Lord Vishnu OR 10 times as devotees of Lord Vishnu. They chose to take birth on earth 3 times. In the first birth (During Satya Yuga), they were born as Hiranyakashipu and Hiranyaksha.