The company (if it is still operating) is responsible. Beyond that it depends on who was considered a “Responsible Person” via a 4180 interview. If the IRS knew that the president (who since left) made the decision not to pay the tax, he or should would likely be held responsible. In addition, unless they were able to prove that they were not responsible and had no way of knowing the taxes were not being paid, the Shareholders/Owners of the company as well as the signatories on the bank signature card would be considered and most likely be held responsible. It is important to vigorously defend your client in a 4180 interview if you believe they should not be held responsible.