There are many stories about the Fire Nation's royal family how they are all insane and bloodthirsty, how it runs in their blood, but there was one royal who was the most terrifying but these skills were hidden under a mask of incompetence and deception. This royal's name was Prince Zuko.
When Zuko was six he accidentally wondered into the dangerous of the Fire Palace and saw a prisoner being tortured using firebending and instruments, immediately he was enraptured he wanted to learn how to do it.
After the torturers had finished their session still not obtaining the information they desired, Zuko walked up to them and asked, "Can you teach me?"
One of them scoffed and said, "No one wants to learn how to torture someone, but if you really want to know then get that prisoner to talk and we'll teach you, okay kid."
"Deal." And with those words he walked up to the prisoner and said, "Start talking or the pain will start." The prisoner only laughed, because after all what could such a young kid do to him. Zuko grinned insanely, "I was hoping you'd do that, now let's begin, when you feel like talking say dragon and the pain will stop." He walked over to the rack of instruments and came back with a long, jagged knife.
"Now let's see, you're a prisoner now you won't be needing fingers." He cut off the right thumb, the prisoner screamed. "Still not hearing the words, don't worry will loosen your tongue yet." And proceeded to cut of the other four.
"Dragon, dragon, please have mercy, I'll talk, please." Zuko turned to the two men with a smile, "So, when do my lessons begin?" After that day Zuko went to the dungeons and learned how to loosen the tongues of people from everywhere. He wore a mask in the shape of a dragon, to hide the fact he was a member of the royal family and the truth of his age. He soon earned the name the Bloody Dragon, and was infamous across the Four Nations for his ability to make anyone talk. Fire Lord Azulon eventually promoted him to the Head of the Tortures, without ever knowing that the person was his own grandson.
When the Fire Lord died and Princess Ursa disappeared, the Bloody Dragon, bathed the dungeons with the blood of the prisoners. But even through it all only the two men who began teaching him ever knew his identity. When he became Crown Prince he had to resign his position as head and only come in when there was an especially tough prisoner to crack. Over the years, he hid his abilities from all his family, even after half of his face was burned off and he was exiled. As he searched for the Avatar he kept with him always a dragon mask splattered with permanent blood stains