(i) The term manufacturer includes any person who produces a taxable article from scrap, salvage, or junk material, or from new or raw material, by processing, manipulating, or changing the form of an article or by combining or assembling two or more articles. The term also includes a producer and an importer. An importer of a taxable article is any person who brings such an article into the United States from a source outside the United States, or who withdraws such an article from a customs bonded warehouse for sale or use in the United States. If the nominal importer of a taxable article is not its beneficial owner (for example, the nominal importer is a customs broker engaged by the beneficial owner), the beneficial owner is the importer of the article for purposes of chapter 32 and is liable for tax on his sale or use of the article in the United States. See section 4219 and the regulations thereunder for the circumstances under which sales by persons other than the manufacturer or importer are subject to the manufacturers excise tax.