PCI-DSS SAQ A is supposed to be signed off by the "Merchant Executive Officer". Who is that?
NOTE : not a QSA, but do have some PCI experience
The merchant executive officer is the officer of the company that has responsibility for compliance/regulatory matters. This is often the Chief Financial Officer, but could be a Chief Security Officer, Chief Technology Officer, even the Chief Executive Officer or Chief Operating Officer.
Who it is depends on the company, but it is likely the "C" level executive to whom the people who handle compliance, certification and regulatory matters reports to.
It's the person who is in charge of the PCI, in any company, who does this as well. In the ideal sense, it's the Merchant Executive Officer of a company who does this. In some companies, it would be the CFO (Chief Financial Officer) who has this additional responsibility as well. Sometimes it's the COO or CEO who handles this as an additional responsibility. Well, all this depends on the size of the company and also on how the hierarchy works in the organizational set-up.