It was developed in the early 1980s and released in 1984. It was the language used by NeXT in its NeXTSTEP operating system. Until the introduction of Swift in 2014, Objective-C was the primary language supported by Apple for developing macOS and iOS applications. Even so, Objective-C is a very stable and well-tested platform, and much of macOS and iOS is still written in Objective-C, so its use is likely to continue for years to come.
Objective-C is a superset of the C language, which means C code can be compiled with an Objective-C compiler, and C code can be freely used in an Objective-C class. It derives its object syntax from Smalltalk while all the syntax for non-object-oriented operations are identical to those of C.