C is a low-level language, and a relatively small language at that.
It was originally written as the language for UNIX at Bell Labs by Dennis Ritchie in 1972, but is not tied to any hardware in particular.
In contrast to its predecessors (B and BCPL), C is not a typeless language. It revolutionized the way programming languages interact with and manipulate data types, and set the stage for years to come.
Dennis Ritchie and fellow colleague at Bell Labs, Brian Kernighan, wrote the original literature and manual on C in the book "The C Programming Language" in 1978.
The second edition (post-ANSI, re-published 1988) is still widely used today, and considered a prime resource on learning and referencing the C Language.
As of today, the language has not changed much since its creation. The ANSI industry standard has been roughly the same since 1989, with some functional changes along the way.
Today, C18 (published in June 2018) is the current reference point and standard for C code, correcting certain errors in C11 (published 2011). However, no changes or features were added to the language
The most important contribution C has made to the world (in addition to helping develop UNIX, which MacOS and Linux are still based on today, and many machines still rely on), has been the foundation it has laid for other languages.
A large swath of languages have been based on C, including but not limited to C++, Python, PHP, C#, Go, Swift, and Objective C.
In addition, a number of languages are derivative or similar to C, while not being strictly based on it.