The repl_publisher login ID is created automatically when a server is set as a subscription server. It allows replication processes on the distributor (which may be a separate distribution server or a combined publication/distribution server) to connect to a subscription server and replicate table schema and data to destination databases. This login ID should not be modified, nor should users use it to log in.
When replication is set up, a subscription server is automatically set up as remote server to its distributor. When replication processes from the distributor connect to the subscription server, they connect using the repl_publisher login ID.
When a database on the subscription server is marked for subscription, the repl_publisher login ID is aliased to DBO on that destination database. This allows replication processes to create tables and schemas, and to perform inserts, updates, and deletes.
It is possible to manually alias the repl_publisher login ID to a user with lesser database privileges than DBO, but this should be done with care because all replicated objects within the database will be created and maintained using this login ID.
For more information about replication, see Part 6, Replication.