The Namokar Mantra was not composed by any one Tirthankar. In Jain tradition, it is an eternal and beginningless mantra that offers reverence to the Panch Parmeshthi:

1. Arihants
2. Siddhas
3. Acharyas
4. Upadhyayas
5. Sadhus

So, no Tirthankar is said to have “recited” it first. It is considered timeless and self-existent in Jain Dharma, not created at a particular time.

If you want, I can also explain:

• the meaning of the Namokar Mantra, or
• the difference between Tirthankar, Arihant, and Siddha.