Who Exactly is Google's Client?

Colin posed this question last night and the more I think about it, the less I seem sure of an answer. Let's take a look at some possibilities:

1) The User- Google provides the search according to what you, the internet user, ask for.
2) The Sites Being Searched- Google provides the sites with an easy way for users to find it.
3) Advertisers- Google provides the platform for advertisers to get their message across.

I'm not even sure that these are all of the possible clients. Each have their own argument to go with them and each seem equally valid. What are some of the other clients that Google is invested in? Do they favor one over the other? Is the user really the main concern for Google or are they siding in a different way? I've got to admit that this question is really fascinating me. Previously, I had always thought that their primary client was me, the user. However, the sites that I'm searching for are being helped nearly as much, if not more so than I am. How else would I find obscure sites around the web? I'm really not sure.