In layman’s terms, prior to May 13, 2019, a responsible party of a limited liability company was any member (or owner) of the limited liability company–even if the owner was another company; and for corporations, the responsible party was generally an officer of the company, such as a President or Vice President.
Furthermore, prior to May 13, 2019, the IRS would accept applications for an EIN even if a responsible party did not have either an EIN, SSN, or ITIN, so long as the application was made by fax by submitting a Form SS-4 and Form 2848.
However, effective as of May 13, 2019, the IRS revised its EIN application procedures as follows:
1-All EIN applications (mail, fax, electronic) must disclose the name and Taxpayer Identification Number (SSN, ITIN, or EIN) of the true principal officer, general partner, grantor, owner or trustor; and
2-Unless the applicant is a government entity, the responsible party must be an individual (i.e., a natural person), not an entity.