Which organization is responsible for the ISA 62443 series of standards?

The ISA/IEC 62443 standards series was originally developed by the International Society of Automation (ISA) and then adopted and published by the International Electrotechnical Commission (IEC) as the IEC 62443 series. The IEC is the primary international body responsible for the ongoing development, maintenance, and publication of these standards, which are recognized globally for IACS cybersecurity. ANSI is a US standards body, NIST is responsible for US federal cybersecurity frameworks, and ETSI develops telecommunications standards for Europe, but IEC is the correct answer here.