Is there any one principle above all which characterizes Jainism?

Yes, the principle of Ahimsa (non-violence) is the most fundamental and distinguishing characteristic of Jainism. Jain philosophy teaches that non-violence is the highest religious duty (ahiṃsā paramo dharmaḥ). Ahimsa in Jainism is practiced not only in action, but also in speech and thought, and is extended towards all living beings, no matter how small. This core principle shapes all other teachings, practices, and ethical guidelines in Jainism, influencing how Jains live, what they eat, and how they interact with the world.