Before Twitter was public, it was just an AIM hack on Jack Dorsey's pager.
Twitter founder Jack Dorsey had a background in messenger culture. He had even launched a dispatch software startup called D-Net, back in 1999. He was also captivated by his friends status messages on AOL Instant Messenger. He wanted to combine the two. And in an era when AIM was king, he did just that.
"I loved seeing at a glance my friends status updates. But I also really appreciated at the same time the dispatch aspect, where you're out in the world doing something away from the keyboard and IM did not allow that," said Dorsey. "I had a RIM pager, the 850, the first email device. I programed a system where I could fire off an email from that and set my status from anywhere. And it worked! And I was able to also at a regular interval pull my buddy list and get those updates sent to my email address. It was awesome! But the number of people who had those mobile devices was so minimal that the timing was just not right. This was 2001."
In 2006, when he was working for Evan Williams at Odeo, Dorsey resurrected the idea. He combined the timeline aspects of LiveJournal with the status updates of instant messenger and the concept of dispatch software that delivers them all remotely. Boom. That's Twitter.