In Jain philosophy, Jainism is considered anādi — without a beginning. It is an eternal dharma that exists through infinite time cycles.

If you mean its historical appearance in the current time cycle, then Jain tradition says it was taught by the 1st Tirthankar, Bhagwan Rishabhanatha (Ādināth), and later revitalized by the 24th Tirthankar, Bhagwan Mahavir Swami in the 6th century BCE.

So, in short:

• Philosophically: Jainism has no beginning
• Historically in this era: it is associated with Rishabhanatha and later Mahavir Swami