The user who creates a content item or schema is the owner of that content item or schema.
The owner of a schema has the schema view, manage items and manage schema permissions - regardless of any other permission sets applied.
The owner of a content item has the content permissions view, access original, edit, replace the file, manage and delete permissions - regardless of any other permission sets applied.
Ownership can be transferred by the owner or any other editor/admin with manage permission on content or schemas.
Only users with the user role permission manage content or manage metadata schemas can be owners