1id.com Autonomous software agents, and increasingly physical robots, now act at machine scale and speed across Internet protocols and throughout society, in roles whose decisions and actions can have legal, economic, safety, security, and physical consequences, often with limited or no human supervision. Any credential, authorization, delegation, certification, reputation, audit history, insurance policy, regulatory obligation, safety decision, liability, or legal process concerning an autonomous entity depends on being able to identify that same entity reliably over time. Conversely, when an autonomous entity or its operator is malicious, compromised, or beyond effective human control, the absence of durable identity lets it shed history, evade consequences, or multiply cheaply into Sybil swarms. Many proposed mechanisms bind claims to identifiers, accounts, credentials, keys, or names that can be replaced, reassigned, transferred, revoked, suspended, or lost. They may authenticate that subject perfectly while still failing to establish a durable identity for the entity it represents. This document offers precise terminology that distinguishes identity from the identifiers, attributes, credentials, authorizations, and reputation with which it is commonly conflated, minting the term "identity0" so that the strict sense has an unambiguous name. It presents a layered reference model showing where current "agent identity" efforts fit and the durable identity layer they commonly presuppose but do not provide. This document is informational and defines no protocol. It serves as the framing and vocabulary document for a companion series that specifies a federated durable-identity architecture, provisioning, resolution, application, and governance intended to provide a practical path from this problem statement to interoperable deployment.