Which organizations help maintain structure and standards on the Internet?

IETF (standards), ICANN (names and numbers), and IAB (technical architecture).

• IETF (Internet Engineering Task Force): Develops and promotes Internet standards
• ICANN (Internet Corporation for Assigned Names and Numbers): Coordinates IP addresses and domain names
• IAB (Internet Architecture Board): Oversees technical development of the Internet

No single individual or group owns the Internet; these bodies coordinate it instead.

Go deeper:

• Internet Engineering Task Force (Wikipedia) — the body that develops the TCP/IP technical standards (RFCs) via open consensus.
• ICANN (Wikipedia) — coordinates the DNS namespace and IP-address allocation — the naming/numbering layer.
• Internet Architecture Board (Wikipedia) — the architectural-oversight body above the IETF.