FORTUNE — Google is becoming all things online. Its quest to organize all the world’s information has pushed it beyond the search box. Google saw that people loved Yelp, so it aggregated reviews. It saw how we took to group-buying deals, so it launched Offers. It chased Facebook for years and finally came up with Google+. It added games to the equation. And now, with its $12.5 billion bid for Motorola Mobility, it is staking a major claim on the mobile web.

It’s as of the company is asking us: Why look anywhere else for your online needs? Google (GOOG) wants to be to the web what Wal-Mart (WMT) was to retailing in the 1990s – or what Amazon (AMZN) has been to retailing in the last decade. It wants to be the only game in town. It wants to be the one domain to rule them all.

It wants, in other words, to be a portal.

But of course, Google won’t say that out loud. In the past, it’s corrected bloggers who dared call it a portal. And its efforts to create home pages (iGoogle, What Do You Love? ) have been uncharacteristically halfhearted. Traditional portals like Yahoo (YHOO) and Microsoft’s (MSFT) MSN  have always paid publishers to syndicate content, while Google simply aggregates what’s published on the web. And it’s a fine line between directing web users to the information they want and co-opting content without paying publishers.

There is another clear reason not to claim to be a portal. It’s the business model that dares not speak its name. Few labels are as unglamorous in the web industry as the portal. It reeks of the primitive 90s, when early mammoths like Lycos, Excite and AOL (AOL) ruled the web. Portals were for newbies, who needed someone to hold their hand while they navigated the web.

But make no mistake. Google is becoming a portal. Google may still draw 98% of its revenue from online advertising. But less and less of those advertising dollars are coming from Google’s iconic search box. They are coming from YouTube ads, they’re coming from Gmail ads and they’ll be coming from newer services like Google+, Offers and Games. All of these initiatives mirror services that are the bread and butter of portals: web mail, online videos, e-commerce and games.

Which is especially strange because Google’s simple search box all but killed the web portal. Rather than roaming inside the walled garden of Yahoo’s domain, say, Google’s search offered the freedom to roam the web at large. Then came Facebook, and Google’s search model seemed doomed to go the way of the portal. So the company brought out Google+, a social network added to the sprawling menu of features that have little to do with search.

Google has faced a second threat to its search revenue — the explosion of mobile apps on smartphones, which allow users to access web content free of search engines. When it debuted, Apple’s (AAPL) iPhone offered a vision of the web where Google simply wasn’t needed anymore.

But Google had Android, a little-noticed acquisition that has quickly become a mobile OS optimized to support Google features like Maps, Wallet and Local. And Google’s purchase this week of Motorola Mobility (MMI) suggests it wants to integrate hardware and software to create a mobile device that, unlike like the iPhone, isn’t independent of Google’s ad-serving products, but greatly dependent on them. The Android phone is a portal in your pocket – and the portal belongs to Google.

At the end of the day, a portal is simply a suite of features combined to create a gateway to web content – whether it’s a web directory like Excite, a cluttered home page like Yahoo or a mobile platform like Android. The goal is to get users to come to you when they want to navigate the web, and to take a cut of the revenue once you help them get there.

To keep growing, Google has to adopt the very business model it started out rebelling against. It has to become that gateway through which we enter the web. Google might as well admit it: It’s fate is to become a portal.