The original Bourne shell, the ancestor to the Bourne-Again Shell (bash) was written in C.
Well, almost.
The original Bourne shell was written in a highly modified version of C (#define anyone?). Bourne called it “Bournegol” and it converts many of C’s structure to Algol-style structure.
#define IF if(
#define THEN ){
#define ELSE } else {
#define ELIF } else if (
#define FI ;}
All of the #defines used can be found here.