If your question is how to write out what you have there, only without the abbreviation of "Company", then you are talking about a possessive- not a plural. " This is for the singular word "company" made possessive, since the founder belongs to the company. If you want plural (more than one) company, then it would by " Smith Companies' founder ," meaning that there are 2 or more "Smith Companies" and you are referring to the person who founded them all.
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