Founder of the comapny
As a rule the founder is a person (legal or private person) who is the first owner of the company at the moment of incorporation. Therefore the founder of the company never changes as the first owner(s) is alaways called founder(s).
Owner of the company
When the first owner (founder) transfers the share to somebody then the founder is not any more the owner, can not act as a shareholder and control the company. Hereinafter only the current owner have full contol over the company and only he can appoint board member(s) (called also board of directors).
Board member (director) of the company
As a rule only board members are lawful representatives of the company. However in small companies usually owners appoint themseleves as board members and therefore it seems that owners (shareholders) can represent the company. If owners (shareholders) are not board members they can only represent the comapny if the board member issues them a Power of Attorney (POA).
A shareholder (owner) who is not a board member exercises its rights only at the general meeting of shareholders.