There isn’t a single person who “decided” the 108 forms or aspects of Parshwanath. In Jain tradition, the number and variety of Parshwanath idols or forms developed gradually over many centuries through temple iconography, local devotion, and ritual practices. Different Jain communities (notably Digambaras and Śvetāmbaras) sometimes recognize slightly different lists or names of Parshwanath forms, reflecting their own historical lineages and devotional customs.

Key points:

• Parshwanath is the 23rd Tirthankar in Jainism.
• The 108 forms or manifestations of Parshwanath arose from long-standing devotional practice, temple art, and sectarian traditions, not from a single codified decree.
• There can be differences between Digambara and Śvetāmbara traditions regarding which forms are emphasized or named.

If you’d like, I can point you to a Jain Knowledge page that discusses Parshwanath and related iconography in more detail.