Bizarrely enough I reckon kshiteej is correct, reading carefully through and specifically "In 1971 I began to extend the B language by adding a character type and also rewrote its compiler to generate PDP-11 machine instructions instead of threaded code. Thus the transition from B to C was contemporaneous with the creation of a compiler capable of producing programs fast and small enough to compete with assembly language. I called the slightly-extended language NB, for `new B.' "

It seems from this that as NB was developed further, there came a point where he decided to call the new language C:

"After creating the type system, the associated syntax, and the compiler for the new language, I felt that it deserved a new name; NB seemed insufficiently distinctive. I decided to follow the single-letter style and called it C"

So the question really hinges on whether or not the compiler itself used the type system and syntax mentioned here. If it did, then the compiler itself would have been a C compiler. So the answer is either C as kshiteej says, or it's NB, if you can't accept the mildly paradoxical view that the first C compiler was written in C.

I guess we'd need DMR's view on the question to be certain what the correct answer is.