This is a light introduction to the unique “decentralized identifiers” (DID) that follows the W3C DID Specification: https://w3c.github.io/did-core. This specification allows any platform to interoperate and use each others identity systems.
It is tied to a unique physical real world entity, including inanimate objects but may also refer to abstract entities.
DIDs alone are useless, they must be verifiable, which is they must have a way to prove they are tied to a certain entity.
A key consideration is that users are still free to use a centralized whitelist of verifiers they trust, which is essential to allow DIDs to gain mass adoption, but does not match the ideals of decentralization.Therefore initially a DID may not be as global as we hope, but over time we do hope some KYC providers gain international acceptance.
To do it properly we need an Autonomic Identity System (AIS) which can be further explored at: https://arxiv.org/abs/1907.02143
A person or unique entity can have more than one DID, this is a realistic approach as people may want to have anonymous personas, or different personas for work, virtual worlds and more.
Of course the most intuitive use of DIDs is for a global decentralized official identity that is recognized by multiple countries and goes beyond a passport with additional verifiable data such as credit worthiness, education, skills and security clearances.
For a person, they should have full control over their identity and what they choose to share. This is related to the self-sovereign identity (SSI) movement - https://sovrin.org/faq/what-is-self-sovereign-identity.
You can find other design decisions by the W3C DID Working Group here: https://www.w3.org/TR/vc-data-model/#use-cases-and-requirements
Think of it like a NFT (non-fungible token) that has a standard way of describing the entity that it is tied to.