What is "viltrumite"

The Viltrumites are a fictional alien race in the Invincible comic book universe. The Viltrumites are native to the planet Viltrum and have constructed, over millennia, a galactic empire known as the Viltrumite Empire. They have superpowers such as flight, enhanced durability, and super-strength. These powers have helped them to subjugate worlds and expand the Viltrumite Empire with ease. They also make use of armed forces from conquered worlds.