Short answers, pulled from the story.
John Michell published a letter suggesting this phenomenon in 1784. He calculated that a star with the same density as the Sun but five hundred times its radius would trap all emitted light.
Karl Schwarzschild found the first exact solution to Einstein's equations just months after Albert Einstein published his general theory of relativity in 1917. His work revealed a critical radius where terms in the equations became infinite though physicists did not understand its meaning at the time.
Researchers independently identified Cygnus X-1 as the first astronomical object commonly accepted to be a black hole in 1971. Louise Webster and Paul Murdin along with Charles Thomas Bolton analyzed data from Greenwich and Toronto observatories showing the source was part of a binary system with the supergiant star HDE 226868.
The LIGO Scientific Collaboration announced the first direct detection of gravitational waves named GW150914 on the 11th of February 2016. Two black holes approximately 1.4 billion light-years away merged creating ripples in spacetime that traveled across the universe.
The Event Horizon Telescope published the first direct image of a black hole's shadow surrounding Messier 87's galactic center on the 10th of April 2019. This event marked a major milestone following the discovery of gravitational waves by Rainer Weiss Kip Thorne and Barry Barish who received the Nobel Prize in Physics in 2017 for their leadership on the project.