Twitter developed Bootstrap as a framework to boost consistency across internal tools as before that various libraries were used for UI development, which led to high maintenance work and a lot of inconsistencies.
During Twitter's first Hackweek the firs deployment in live conditions took place. During this event Mark Otto one of Boostrap's developers showed some collegues how to speed up their progect's development with the aid of this tool.
Twitter has released Bootstrap in August 2011 as open source, while in February 2012 already became the most popular GitHub project.
The configuration of Bootstrap offers a "Customize" option in the documentation since version 2.0 of the toolkit packing an intuitive and strong front-end framework for faster web development.
Tool's 3.0 version brings a rewritten project making it mobile friendly from the start, so mobile first styles can be founded through the whole library instead of in separate files.