the mysterious Undead

the undead are an anomaly in this world. the have many interesting abilities and powers, while many paladins use the power of the light the undead use the power of death that is why they are often called "death knights". they are said to come from one mysterious being named the "death king". the death king also known as "sealazar" is a mysterious being as he was foretold to have been an angle who went against the wrath of God, sealazar, and his brother azultazir were a very strong duo feared by both angels and demons alike. but on one particular day, the angles saw some sort of a black hole they called it "the void". it was said to have a very powerful presence to it, many angles thought that it was a test from god so they left it away but many angles defected and went inside the portal one of them was azultazir. after passing through the portal many angles became mad and insane. no one could have stopped them ravaging and killing of the angles except one person sealazar, while all of the other angles were thinking of none violent ways on how to bring them back sealazar was the only one who stood against them and killed all of them. after his massacre, it was revealed that the void was a test from God, God wanted to test the loyalty of the angles by creating the source of all power available for them to take, but it has been said that God never expected someone to be so strong that he can slay angles even after they go through the void. after the whole ordeal, God banished sealazar to the realm of the dead and took off his wings so he can't escape his fate. sealazar was giving the title of "the ruler of death" by the angles which later became the "death king" by his followers.
the undead are as to folklore are souls that have not achieved their goal or ambition. so the death king grants them one more chance in life to achieve that goal in exchange for taking their soul away. the death king's goal is to die by the hand of death but death refuses to as per God's request. so the death king tries to steal as many souls from death as he could in hopes of death ultimately killing him one day.
the undead, however, have been in the ether world since the beginning of time however every undead was prohibited from joining azir during the light age nonetheless they did participate the allied races during the the extinction age . 
the undead have declined throughout history. but many humans worship the death king as their god in exchange of being granted powerful abilities.