Rituparna (IAST): Rituparṇa was a king of Ayodhya, and son of Sarvakama, into whose service king Nala entered after he had lost his kingdom. Rituparna was a master mathematician and profoundly skilled in dice Kali (Demon). Nala, as Bahuk (one with a hump) became a minister and later the charioteer in King Rituparna's court on the advice of the King of Snakes (Nagas) to learn from him the skills of dice.
According to the story of Nala-Damayanti of Mahabharata, after the disappearance of King Nala, his queen, Damayanti and her father's (the father-in-law of King Nala, the king of Vidarbha Kingdom) courtiers sent out a search party to find him. One of the courtiers reported a person "resembling in behaviour, but not in features" with Nala in King Rituparna's court in Ayodhya. To test this fact it was proclaimed that Queen Damayanti (known for her beauty) had assented to remarry, and consequently an invitation to a swayamvara for the same was sent to Rituparna's court too. However the swayamvara (a ritual wherein a princess bride chooses her own suitor for marriage from among a group of suitors), was scheduled for the very next day, and the distance to her father's kingdom from Ayodhya could not be covered in a night. For this Nala as Bahuk offered to transport King Rituparna to Damayanti's kingdom. As Nala was the best charioteer Nala he was sure to reach Damayanti's father's palace in time for the swayamvara. On the way King Rituparna asked Nala or Bahuk, as he was known to him, for the secrets and techniques of fast chariot driving. Nala agreed but in return for which he asked the knowledge and techniques of dice playing, in which Rituparna was the master. Thus on a mutual acceptance, within a night's journey Rituparna taught Dice-playing to Nala and Nala taught him chariot driving skills.
On reaching Damayanti's father's palace, however, king Rituparna was informed that the swayamvara was a sham and actually a ploy to find Nala, who indeed came back to his own form from that of Bahuk using a boon from the snake king (king of the Nagas). And using the art of Dice learnt from Rituparna in the previous night's journey, Nala defeated his brother Pushkara in dice and became the king of Nishadha Kingdom again.
The story does not cite anything else about King Rituparna after this episode (Nala being re-crowned ruler of Nishadha Kingdom).