If Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL) were a person, it would now be able to legally do a host of things in the United States that it wasn't able to do just yesterday without running afoul of the law: buy alcohol and gamble in all casinos, to name a couple.

Yep, the search-engine giant turns 21 today! The company was founded on Sept. 27, 1998, in Menlo Park, California.

In honor of Alphabet's birthday, here are 21 reasons -- in no particular order -- to buy shares of this giant tech stock.

Two lit candles -- a 2 and a 1 -- in a cupcake surrounded by colorful curly paper streamers on a blue background.

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1. The company is run by a founder

Alphabet CEO Larry Page is one of the company's two co-founders. Studies show that the stocks of founder-led companies tend to outperform in the market.

2. Its stock has outperformed over the long term

Indeed, Alphabet's stock has been a long-term winner. Over the last 10 years, shares have gained 405% (through Sept. 26), easily outpacing the S&P 500's 251% return.

3. Its stock has recently gained steam

Google Class A and C shares have performed about on par with the overall market so far in 2019, but their recent momentum has been strong. Over the last three months, shares of both classes have jumped about 15%, thanks to the company's second-quarter earnings breezing past Wall Street's expectations.

4. It's the market leader in digital advertising

Google and Facebook (NASDAQ:FB) -- in that order -- are the two 800-pound gorillas in the global digital ad market, a lucrative space that's growing rapidly. Amazon (NASDAQ:AMZN) is a distant third.

5. It dominates the U.S. search-engine market

In August, Google sported an 88% share of the U.S. search-engine market for all platforms.

6. It has an even greater lock on the global search-engine market

Also in August, Google had a whopping 92.4% share of the global search-engine market.

7. Analysts expect its solid earnings growth to continue

Wall Street projects that Alphabet will grow earnings per share (EPS) at an average annual rate of 12.6% over the next five years.

8. The company frequently beats earnings expectations

Alphabet has a good track record of exceeding the Street's consensus earnings estimates, so there seems to be a strong chance that it will continue to do so. In other words, the 12.6% growth rate expectation could prove too low.

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Image source: Getty Images.

9. It's gaining ground in the cloud computing market

Google is the third-largest provider of cloud computing services behind Amazon and Microsoft (NASDAQ:MSFT). Along with Microsoft, it's been gaining ground in this fast-growing space. In the second quarter, Google Cloud captured a 9.5% share, up from 8.7% in the year-ago period, according to Canalys, which estimates that the entire global market grew nearly 38% to more than $26 billion.

10. It was an early mover in using AI

Google was an early mover in using artificial intelligence (AI) and continues to expand the use of this tech to improve its primary advertising vehicles, search and YouTube, and other businesses. In 2015, for instance, the company began using its RankBrain AI system to better understand some search queries, among other things.

11. Its Waymo autonomous vehicle subsidiary is now generating revenue

Alphabet has begun monetizing Waymo, the pioneer in self-driving vehicles. Late last year, the company launched, in a limited manner, its first self-driving car service, in Phoenix, Arizona. Once driverless vehicles become legal across the country, Waymo could become a significant contributor to the company's growth.

12. It's a major player in the rapidly growing smart-speaker space

In the second quarter, the company's Google Home smart speaker lost market share. Nonetheless, Google is still the third-largest player, behind Amazon and Baidu, with a market share of 16.7%. In Q2, this global market grew by more than 55% year over year to reach more than 26 million units shipped, according to Canalys.

13. Its "other bets" provide it with upside growth potential

Alphabet's "other bets" segment -- formerly called Moonshots -- is essentially a business incubator, nurturing a host of diverse businesses that could potentially become notable contributors to the company's sales and profits in future years.

14. It's immensely profitable

Alphabet has a fat 23.4% profit margin for the trailing-12-month period. That slightly trails Facebook's 27.3% but is a bit better than Apple's (NASDAQ:AAPL) 21.5% and much higher than Amazon's and Netflix's (NASDAQ:NFLX) profit margins of 4.8% and 6.5%, respectively.

A huge pile of $100 bills.

Image source: Getty Images.

15. It has a huge pile of cash

Alphabet had $121.1 billion on its balance sheet at the end of the second quarter.

16. It has little debt

The company had $14.2 billion in debt at the end of the last quarter.

17. It should be fine if Page retires early

While co-founder Page is just 46 years old, it's not uncommon for billionaire business leaders to retire early from their corporate gigs to do philanthropic work and/or just have more time to enjoy their money. Microsoft founder and former CEO Bill Gates, for instance, stepped down as CEO when he was just 44 before giving up his chairman role some years later.

Alphabet should be OK if Page leaves his post early, even abruptly. Sundar Pichai, who leads Google, should be able to step in relatively seamlessly as Alphabet's interim leader. Google, after all, contributes the vast majority of the company's revenue and all of its profits.

18. Employees like working for the company

On Glassdoor.com, Alphabet employees and former employees give the company an overall rating of 4.4 stars (on a scale of 1 to 5). Employee satisfaction is important for all companies but particularly for tech companies, as there is a limited amount of top tech talent. (Note that the 4.4 rating is listed under Google.)

19. Employees are more satisfied than those of most of the other big techs

Many top tech companies draw from the same talent pool, particularly those located in Silicon Valley. So it's a plus for Alphabet that its employees are more satisfied than those of Apple and Netflix, which garner overall Glassdoor ratings of 3.9 and 4.0, respectively. Along with Alphabet, Facebook, also located in the same region, scores a 4.4. Amazon, which is headquartered in Seattle, garners 3.8 stars overall.

20. It's the only "FAANG stock" that's been less volatile than the overall market

Google's two classes of stock sport three-year betas of about 0.95, which means they've been about 95% as volatile as the overall market over the last three years. Facebook, Amazon, Apple, and Netflix all have three-year betas above 1.0, reflecting volatility greater than the broader market. (FAANG = Facebook, Amazon, Apple, Netflix, and Google.)

21. It's a 5-star stock on Motley Fool CAPS

Alphabet stock garners five stars (on a 1-5 scale) from our CAPS community, with the best-performing members, the CAPS All Stars, particularly bullish.