The first black hole directly imaged by the Event Horizon Telescope was M87*.
M87* is the supermassive black hole at the center of Messier 87, a giant elliptical galaxy about 55 million light-years from Earth. The Event Horizon Telescope (EHT) combined radio observatories around the world using very-long-baseline interferometry, creating an Earth-sized virtual telescope capable of resolving structures on the scale of a black hole's surroundings.
The EHT collected the relevant observations in April 2017 and released the image on April 10, 2019. The famous orange ring is glowing emission from extremely hot plasma around the black hole; the dark center is the black hole's shadow, produced as gravity bends and captures light. The observation provided a dramatic test of general relativity in a strong-gravity regime.
M87* is often confused with Sagittarius A*, the black hole at the center of our own galaxy. Sagittarius A* became the second black hole to be imaged, with its first EHT image released in 2022. GW150914 was the first gravitational-wave black-hole merger detection, while Cygnus X-1 was an earlier strong candidate identified through stellar and X-ray observations.