With most startups, the incorporator elects the initial board of directors after the certificate of incorporation has been filed. The incorporator can elect him or herself to the initial board of directors. The incorporator typically executes a document called an Action of Incorporator (also called an [Initial] Action by [the] [Sole] Incorporator), in which the incorporator adopts bylaws for the corporation, sets the size of the board of directors, and elects the initial board of directors. The role of the incorporator ends there.
It usually doesn't matter who the incorporator is, primarily because the corporation has no assets at the time of incorporation. If the incorporator elects an initial board of directors that his or her co-founders disagree with, they can simply incorporate a new corporation on their own. For this reason, the incorporator for a startup is typically the founder who is most willing to handle the paperwork. Some law firms have a paralegal or attorney serve as the incorporator.