What is IANA?
While IP Addresses may not be formally "owned" by anyone, this does not mean that everyone is free to use whatever IP Addresses as they see fit as when it comes to something the size of the Internet, this would produce nothing but chaos if people just did anything they wanted.
For most people who want to build private home or office networks, there are blocks of private IP addresses that are reserved for use by anyone but when it comes to real, global IP addresses, there has to be some sort of ordering scheme for their allocation and in the case of the Internet, there is a single, worldwide process for this that begins with the Internet Assigned Numbers Authority or IANA.
The Internet Assigned Numbers Authority is a US-based organization tasked with overseeing the allocation of IP addresses in a fair and consistent manner that benefits everyone. With a total number of over 4 billion addresses this is somewhat impractical for one organization, so IANA has broken down this function by assigning large blocks of addresses to what are known as Regional Internet Registries, or RIRs. Each registry takes charge of looking after the IP addresses assigned to their region on on behalf of IANA and for the good of the Internet and it's users.