Every year since 2002, Google has put up a different Google Doodle on Sept. 27 to celebrate its birthday, and today is no different. Visit Google.com today and you will find a new retro-style Google Doodle. The scene, which has a Claymation look to it, depicts Google sitting in front of a table with presents, balloons, cards, and of course, birthday cake.

Today marks the 13th birthday celebration for the search engine giant, but most fans would be surprised to learn that today is not actually Google's birthday. In fact, this date has no real significance. Google bought its domain name officially on Sept. 15, 1997, and filed for incorporation on Sept. 4, 1998. September 27 just happens to be the day Google chose to drink and eat cake.

Google, now one of the world's biggest and most influential companies, has come a long way in 13 years. Originally, Google was just a research project between two PhD students at Stanford University, Larry Page and Sergey Brin. The two students theorized a search system that could analyze the relationships between websites, and where a website's relevance to the search terms was determined by the quantity and importance of those pages. This technology was later called PageRank.

Page and Brin's search engine was originally nicknamed BackRub, since the system would check backlinks to estimate the importance of a site, but was later named after a misspelling of the word googol, which is defined as a very large number, specifically 10 to the 100th power. Googol was supposed to be a name that would be indicative of the titanic amount of information on the Internet that the company sought to organize.

Page and Brin registered the domain name Google.com on Sept. 15, 1997, and the company was incorporated on Sept. 4, 1998. Google's first employee was Craig Silverstein, a fellow Stanford PhD student, and the company's first office was actually a garage in Menlo Park, Calif., which belonged to their friend Susan Wojcicki. Wojcicki is now senior VP of product management and engineering at Google, and she is No. 16 on Forbes Magazine's List of the World's 100 Most Powerful Women in 2011.

Google's first investor was co-founder of Sun Microsystems Andy Bechtolsheim, who donated $100,000 to the company in August 1998 before Google was even incorporated. The following year, Brin and Page tried to sell their company to Excite CEO George Bell for a measly $1 million, but Bell, without a crystal ball, rejected the offer.

Google loves to acquire companies. Since 2001, the company has acquired 103 separate entities in a 10-year timespan, including map and traffic analysis companies, mobile software companies, daily deals companies, and even companies developing voice and facial recognition software. Many of these absorbed companies have resurfaced in the form of Google brands, such as Google Maps, Google Places, Google Voice, and Google Offers.

Google's two most valuable purchases, however, came in August 2005, when Google purchased the initial developer of the Android software for $50 million, and in October 2006, when Google bought YouTube for $1.6 billion.

Lately, Google has been focusing on mobile solutions, such as the Google Wallet, and various renewable energy projects, such as solar solutions, wind farms, and the world's first seawater-cooled data center.

Google runs more than one million servers in data centers around the world, and processes over one billion search requests every day. The company made nearly $30 billion in revenue in 2010, but has recently been the target of several antitrust accusations.