December 2012 -- Pope Benedict XVI joined Twitter as @Pontifex, becoming the first pontiff to do do. His successor, Pope Francis, has continued the papal account, which now has almost 3 million followers for the English language account, and 3.7 for the Spanish Twitter handle, @Pontifex_es.
January 2013 -- Twitter users in Japan and Korea set a record by posting 33,388 tweets per second in their time zone as the New Year dawned on January 1.
January 2013 -- Justin Bieber dethroned fellow pop star Lady Gaga to become the most followed person on Twitter. The Biebs now has more than 44 million followers.
January 2013 -- Twitter launched Vine, an app that lets users shoot and share 6-second looping videos. It has since acquired more than 13 million followers, who fill their followers' feeds with delightfully strange video creations.
February 2013 -- The Super Bowl was already one of Twitter's annual high points, when would-be wits unleashed some of their best 140-character one-liners. But this year, when a racy Beyonce halftime show was followed by a 35-minute power outage, things went into overdrive. At the peak, there were more than 268,000 tweets per minute -- and more than 24 million for the entire game.
April 2013 -- Hackers from the Syrian Electronic Army took over the Associated Press Twitter account and posted "Breaking: Two Explosions in the White House and Barack Obama is injured." It was one of the most high-profile Twitter hacks to date and had far-reaching ramifications. The Dow Jones Industrial Average plummeted dramatically before rebounding when the hoax was exposed.