BitKeeper had been used for the version control requirements of the Linux kernel project. Mackall decided to write a distributed version control system as a replacement for use with the Linux kernel. This project started a few days after another project called Git, initiated by Linus Torvalds with similar aims<p>Source: wikipedia<p>Interestingly, both picked negative names.
Git: simpleton, contemptible
Mercurial: in the sense of fickle