An identity and authentication platform utilizes a data model that enables multiple identities such as e-mail addresses, mobile phone numbers, nicknames, gaming IDs, and other user IDs to be utilized as aliases which are unique sub-identities of a main account name. A user may utilize the aliases supported by the platform to project multiple different on-line identities while using the authentication credentials of the main account. The platform is configured to expose the aliases to various client applications and Internet-accessible sites and services such as e-mail, instant messaging, media sharing, gaming and social networks, and the like, to enable the implementation of a variety of usage scenarios that employ aliases.