Who maintains the Internet?

Technically, everyone that is on the internet, runs it. The Internet is just a bunch of computers wired together. There are Internet providers who have many, large fast connections to other providers. Some people call the links between providers the backbone. (From Atlanta to New York City is one of the largest, fastest connections in the world.)

If there was any organization close enough to say they "run" the Internet, it could be Cisco or IANA.

google is also becoming a juggernaut for controlling content and advertising on the web. google provides so many services to so many companies, a large majority of the online market is so dependent on google, that if google went under, most of the online market would go with it.