Who is the Internet Assigned Numbers Authority?

In Summary:

The Internet Assigned Numbers Authority is the organization that coordinates the assignment of all unique protocol identifiers used on the Internet. Identifiers include IP (Internet Protocol) addresses and domain names.

The IANA delegates much of the actual work to various regional organizations throughout the world, such as the InterNIC and APNIC. Each of these groups is responsible for different registrations, such as second level domain names or top level country domains.