The Estronii are an ancient species that date back to the Dark Times.
The Estronii are made of durable rock, which is made of an unknown element found nowhere else in the Universe. This makes them virtually indestructible, being resistant to bullets and lasers. They are humanoid, but very bulky and overshadow most species in height. They are also covered in spikes, and their armour is a part of their skin.
Each Estronii has a crest, which is used to send signals to other Estronii and to support their large brains. Even their organs are made of rock. They are also a very longlived species, for one individual could live over a few millennia. They are very agile, and naturally extremely strong. Females are slightly more slender than the males, but are equally as strong. Estronii lay eggs of stone, and the young have to use their spikes and strength to break the tough shell.
The Estronii are known to be very forceful, and run their colonies and conquered worlds like dictators. They believe to be superior in many aspects, but in recent tims were forced to tone down that attitude, especially when dealing with the Shadow Proclamation and trade empires.
The Estronii evolved from sentient rocks, found nowhere else. They have lived since the dawn of time. During their primitive days, they invented music which later became known as heavy metal. When they developed space travel, Estronii warriors forced their musical tastes on many species, being considered barbarians (since they adapted a penchant for looting and plunder). One covert starfighter managed to find Earth and inspire heavy metal, however it didn't become the world's most popular music.