Should the DYNSA user be listed as user under company db > security > users

In sql when I look at the users of a company db via security > users I don’t see the dynsa user listed. If the dynsa user is the dbo of the db shouldn’t it be listed?  When I look at server login > user mapping  dynsa is listed and when I click on a company db it shows the dynsa as dbo owner of that company.  But dynsa is not listed when you go to the company db security > users.  Normally when you create a login and under user mapping check off a company db then go to the db and look under security > users you see the user listed.