In the days when processing power was expensive, writing assembler code was the benchmark, and high level languages were seen as an extravagance, C was a revelation. Near-assembler fast, bit-level operations, but still an expressive 3GL.
Wait, that’s only the beginning of the story.
With its unique advantages, C quickly became ubiquitous, and C compliers appeared on every computer and OS. Then over time, as the cost of processing power fell, and all programmers began exclusively using high level languages even for realtime applications, C’s real value emerged from that ubiquity: C was the only truly platform-independent programming language. By 1990, you could write a C program and run it on any computer in existence.