I agree with Terrapro, if you are an LLC you are technically the owner. An LLC is a company not a corporation.
So, if you are a corporation you are technically the President
If you are a sole proprietorship or an LLC you are technically the owner.
If you are a partnership you are officially a partner until you go out of Business.
If you have no business format, work for cash and don't pay taxes your official title is crook
You can have more than one title with a corporation.
If you feel a title like President is pompous you don't need to put any title on your business card. You could also appoint yourself manager and put that on the card if you wanted to show you are the person capable of making decisions but don't want to do that in a pompous way.
In the case of a corporation and in the event of insolvency or other risks using the wrong title on a business card would not be enough in itself to pierce the corporate veil. They are going to look much harder at co-mingling finances but it could be an extra nail in the coffin.