First Unix was written in asm. Then Ken came up with B to write some userland stuff more easily. B was not portable. B was a BCPL-like, but smaller and simpler.

Then Dennis came up with C. C was just portable B (it added types for the purpose of getting around the fact that word sizes differed between archs). And then the B code was recompiled with C and modified as needed. Though C is back-compatible to B somewhat (hence why C has the thing where no type implies int).