Rushabh dev (Rishabhanatha, Adinath) is traditionally described as the first Tirthankara of Jainism. There is no fixed Gregorian birth date for him.

• Birth place and parents: Ayodhya (Vinita), to King Nabhi and Queen Marudevi.
• Timing: He is said to have lived millions of years ago, in the very ancient Krita/Satya age, not in historical BCE/CE years.
• Traditions: Śvetāmbara and Digambara traditions agree on the basic facts (birth in Ayodhya, first Tirthankara) but differ on some details and festival associations.

A well-known festival linked to his life is Akshaya Tritiya, which marks the day he first took food after renunciation (his "first meal" after austerities).

You can read more here