How to display the created by value from a SharePoint list on an InfoPath form
Both SharePoint lists and libraries have a column in which the name of the user who created the item or document is stored.
Where SharePoint lists go, you can add a data connection to a SharePoint list and then include the Created By field as one of the fields in the InfoPath data source. You can then access this field on the InfoPath form the same way you would access any other field from a secondary data source.
Where SharePoint libraries go, if you want to retrieve the name of the user who created the form that a user currently has open, you can use a similar technique as described in Display who last modified an InfoPath form in a SharePoint form library, but then use the Created By field instead of the Modified By field.