Is the purpose of the Board and CEO to serve each and every shareholder equally?
They are responsible to the shareholders' interests as a group, not individually (rather clear in case law). However under management ethics they are also responsible to stakeholders at different levels depending on their interests and effects on the interests (with the purpose in the long term still being the shareholders' interests).
It gets much more tricky with different shareholder classes and changes that may alter their effectiveness but that is not so much a day to day issue.