If you're working in an environment as a developer without sysadmin privileges, and you are creating database diagrams using Management Studio underrated diagram tool, but not the database owner or a sysadmin, you'll see your created diagrams look like this
where the diagram is owned by the developer using the sql login 'jdoe'. With many diagrams created by multiple developers, this can be ugly, confusing and just nonsensical. Sysadmins don't have this problem, which is why like me you may have used Database Diagrams for years without encountering this issue.
There is no way to change this or rename it from the Management Studio GUI, but a simple script can fix the problem.
Find the diagram you want to rename, and the new principal you want to be the "owner".
This script can be executed by the developer to change the owner of the diagram from jdoe to dbo.