"You pest! I should have made sure you were dead!"
Quartz is the commanding officer of the changeling army, and is responsible for period historians call the Era of Darkness. His military genius allowed the changelings to conquer half of the known Equestria 1,000 years ago. Until a young pegasus who had a odd magical ability stepped in to save a town from being his next victum. Angered by this intrusion Quartz was set to do battle with the new comer until the alicorn princesses arrived, then he fled. News of that same pegasus spread across the land taken back the territory the changelings had over the years. Quartz took it upon himself to finally put an end to this hero and tracked him to the north. Confronted with his target named Shadow Steed. Quartz buried him under the snow hopfully killing him. 1,000 years later word of the same hero had returned. Astonished at this Quarts vows to finish him if they ever get the chance to meet again.
Quartz is the soon to be husband of Queen Chryisalis he proposes to her by trying to conquer all of Equestria
Quartz sees Shadow steed as a pest but soon thinks of him as a worthy person to fight against. Thats one reason Quartz still hasn't killed him.
Quarts was a normal Unicorn named Quan Shi who was turned into a changeling by an source of dark magic. Quartz and Shadow Steed are seen as opposites. Although both being mutants of their own kind. Quartz powers are tied to his experience of war and Shadow Steed's are tied to his emotions