Answer : 4. "सोमदेव "
Explanation :

Kathasaritsagar is India's unique contribution to world narrative literature. This is a seminal text of Sanskrit fiction, which was composed by Kashmiri Pandit Somdev Bhatt. 'Kathasaritsagara' is also called 'Brihatkatha' of Gunadhya. It was first written in the Prakrit language. 'Vrihatkatha' is the most influential book on the tradition of Sanskrit literature. Gunadhya is considered as respectable as Valmiki and Vyas.