Atithi was son of Kusha and his Chief Queen Kumudvati. He succeeded at the throne of Ayodhya after death of his father Kusha. He had married a Princess of Nishadha Kingdom (somewhere in Himalayan plateau) and also named his son and successor Nishada in her honour.
Kumudvati
Kumudvati was second wife of Kusha but his Chief Queen. She was a Naga Princess and sister of Naga King Kumud. She had eight sons and the eldest son was Atithi. She also had one daughter with Kusha named Champakmalini.
Kusha’s first wife was Champika, daughter of King Bhurikirti of Eastern lands. She gave birth to nine daughters and one of them was named Hema, who became Queen of Avanti.
Atithi was handsome, patient, wise, charitable and a good administrator. He was known for his charity and making the kings he defeated as his vassals.
Source- Ananda Ramayana and Raghuvansh by Kalidas