I think the Doom engine was written in C (and assembler), but the level-editing tools were in Objective-C. Again, the right tool for the right job - Objective-C

I think the Doom engine was written in C (and assembler), but the level-editing tools were in Objective-C. Again, the right tool for the right job - Objective-C's dynamic dispatch greatly helps user interface programming compared to bare C, whereas the Doom engine probably had no need for it.