| SAN FRANCISCO
SAN FRANCISCO Twitter, the 140-character messaging service favored by everyone from the Pope to U.S. President Barack Obama, began as a side-project but rapidly morphed into one of the most powerful social and cultural media forces of our time.
After eight years of explosive user growth marred by persistent technical challenges and management shake-ups, Twitter is now preparing to go public in Silicon Valley's largest initial public offering since Facebook Inc's last year.
March 21, 2006: Co-founder Jack Dorsey sends the first tweet: "just setting up my twttr."
Twitter is a side project within Odeo, a struggling podcasting company where Dorsey worked as a software engineer alongside Twitter co-creators Noah Glass and Biz Stone. The length of tweets are capped at 140 characters in order to include a user's name and still fit within the 160-character SMS messaging format used by mobile phones.
October 25, 2006: Evan Williams, CEO of Odeo, forms a company called Obvious Corp, which acquires all of Odeo's assets, including Twitter.
March 2007: Twitter stages a big promotion at the South by Southwest conference in Austin, Texas, lining the hallways with flat-screen panels that display a constant stream of Twitter messages. The service gains a loyal following among influential bloggers and tech enthusiasts that will prove key to its future growth.
April 2007: Twitter is spun out as a separate company, with co-founders Dorsey, Williams and Biz Stone. Dorsey is appointed CEO.
March 2008: Twitter has 1.3 million users, according to media reports at the time.
October 2008: Williams replaces Dorsey as Twitter CEO. Dorsey, who becomes Twitter Chairman but is no longer a Twitter employee, later recalls in Vanity Fair magazine that it felt like he was "punched in the stomach."
November 2008: Twitter rebuffs a $500 million acquisition offer by social networking powerhouse Facebook, according to media reports. Twitter has about six million registered users around this time.
April 2009: Oprah Winfrey joins Twitter. Ashton Kutcher becomes first celebrity to amass 1 million followers on Twitter. Twitter's total number of registered users reached 14 million the previous month.
June 2009: The U.S. State Department asks Twitter to delay a planned upgrade to its system that would have cut daytime service in Iran. The State Department stresses Twitter's importance as a communications tool during protests following Iran's disputed presidential election.
That request drove home Twitter's growing clout as a communications tool, with global political ramifications.
September 2009: Twitter raises $100 million in funding, in a deal that values the company at $1 billion. Dick Costolo, a former comedy-improvisational actor who later worked at Google Inc, joins Twitter as Chief Operating Officer. Starts new job by tweeting: "Task #1: undermine CEO, consolidate power."
April 2010: Twitter announces test of "promoted tweets," its first advertising product, with six advertising partners including Starbucks and Virgin America. Twitter says it has 105 million registered users and is adding 300,000 new users a day.
October 2010: Costolo replaces Williams as CEO. Williams says he will focus on product strategy.
September 2011: Twitter expands advertising service, letting marketers show a brand's promoted tweets to all Twitter users rather than only to Twitter users who follow the particular brand.
December 2011: Saudi Prince Alwaleed bin Talal buys a $300 million stake in Twitter by purchasing shares from existing investors; Company is valued at roughly $8 billion at the time.
December 2012: Twitter reaches 200 million monthly users.
September 12, 2013: Twitter announces it has filed for an initial public offering.
October 3, 2013: Twitter public files its S-1 statement, giving investors their first view of the company's financials and other key details.
(Editing by Edwin Chan and Bob Burgdorfer)