The concept of black holes was first theorized by John Michell in 1783 and later by Pierre-Simon Laplace in 1796. However, the term "black hole" wasn't coined until the 1960s.

Here's a breakdown:

* John Michell and Pierre-Simon Laplace independently proposed that if a star were massive enough, its gravity would be so strong that even light wouldn't be able to escape. They called these objects "dark stars."

* Karl Schwarzschild in 1916, using Einstein's theory of general relativity, calculated the radius around a massive object within which nothing, not even light, could escape. This is now called the Schwarzschild radius.

* Robert Oppenheimer and his colleagues in the 1930s further explored the theory of black holes and demonstrated that they could form from the collapse of massive stars.

* The term "black hole" was coined in the 1960s by John Wheeler, popularizing the idea and cementing it in the public consciousness.

So, while Michell and Laplace first conceived of the idea, it was the combined work of many scientists, including Schwarzschild, Oppenheimer, and Wheeler, that led to the modern understanding of black holes.

It's important to note that we haven't directly observed the interior of a black hole. We can only observe their effects on surrounding matter and light. However, with the help of telescopes and other advanced instruments, we are constantly learning more about these fascinating objects.