Git was developed as an OSS clone of BitKeeper (which was originally provided freely to Linux kernel developers under the agreement that they not develop a clone).
Git was not developed as a clone of BitKeeper, it has a very different design (snapshot-based content-addressed filesystem, versus the SCCS "weave"). If anything, git was a (much faster) clone of Monotone, minus the heavy cryptography focus which made Monotone so slow.
https://en.wikipedia.org/wiki/BitKeeper