Hades is the Greek god of the underworld, which is like a big dark place where people go after they die. It's kinda like a spooky underground home where Hades lives and rules over all the spirits and souls of people who have passed away.
In Greek mythology, people used to believe that when someone died, their soul would go to the underworld where Hades would decide what to do with it. If they were good people, their soul would go to a happy place called the Elysian Fields. But if they were really bad people, their soul could be punished and go to a really bad place called Tartarus.
Hades was a pretty important god to the Greeks because they believed that afterlife was really important. They thought that if you lived a good life, then you would go to a good place after you died, but if you were bad, you would go to a really horrible place. Hades was the one who made that decision, so people respected him and were scared of him too.
Some people think of Hades as a scary god because he's in charge of everything that happens after someone dies, but others think of him as a powerful and important god because he is responsible for justice and making everything fair for everyone.