BitBake drew inspiration from the Gentoo package management tool, Portage. Gentoo has a unique philosophy of building binaries on the system where they are supposed to run, so that maximum optimizations can be applied to the code. This philosophy fits best in the case of embedded systems, where you always have a different set of hardware in hand, and you need to prepare board support packages for that hardware. Initially, BitBake was a part of OpenEmbedded.
Later on, an OpenEmbedded project team member, Chris Larson, split it into two separate pieces:
Now, BitBake is the base for OpenEmbedded and Yocto Project, which are being used to build and maintain multiple Linux distributions.