CodeIgniter was originally developed by Rick Ellis (CEO of EllisLab, Inc.). The framework was written for performance in the real world, with many of the class libraries, helpers, and sub-systems borrowed from the code-base of ExpressionEngine.
It was, for years, developed and maintained by EllisLab, the ExpressionEngine Development Team and a group of community members called the Reactor Team.
In 2014, CodeIgniter was acquired by the British Columbia Institute of Technology and was then officially announced as a community-maintained project.
Bleeding edge development is spearheaded by the handpicked contributors of the Reactor Team.
A hat tip goes to Ruby on Rails for inspiring us to create a PHP framework, and for bringing frameworks into the general consciousness of the web community.