A linguist translated the name from Protoss writings. A scientific officer convinced Arcturus Mengsk to exploit the psi-enhancing gas for military applications. Mengsk created Project Shadowblade, putting it under level nine classification. The project was led by General Horace Warfield.
This program was responsible for the creation of the first Spectres, Ghosts that had been exposed to the Terrazine gas. The gas was tested on animals, some condemned prisoners, and eventually several volunteers, some of who were low-level psychics. The gas increased psychic power, but it was addictive and created hallucinations and violent outbursts, which often resulted in the injury of project staff.
Over time, Arcturus Mengsk grew leery of the project and ordered its termination. After Warfield was recalled, Mengsk sent in marines to eliminate the project members, ensuring that the project wouldn't be carried on. Others argue one of the spectres experienced severe hallucinations and killed the project members himself. Whatever the truth, only three other members besides General Warfield survived and were all three thrown into New Folsom to hide the truth.
In 2503, a second incarnation of Project Shadowblade launched a rebellion with the intent of killing Mengsk. This was thwarted by Ghost agent Nova Terra and the new Project Shadowblade, while damaged, is not destroyed. Gabriel Tosh picks up where he left off the following year during the Second Great War, having discovered that the element Jorium is good for balancing out the addictive and hallucinogenic properties of Terrazine when used in tandem with a Psionic Waveform Indoctrinator. This allowed him to create new Spectres with lower risks.
But in this day and age, the Spectres and Dominion don't play well together and the Spectres have a deep seated hate of all things Arcturus Mengsk. Tosh, along side Raynor's Raiders, wages a war against them, but behind the scenes are the Spectres, fighting their own war with Dominion Ghosts who are hunting them in an effort to destroy Shadowblade. Which side will you pick? The Ghosts, a tried and true psionic warrior who puts fear into the heart of the Dominion's enemies, or the Spectres, the next generation who give nightmares a whole new meaning.
EDIT: Disc in the title is short for Discussion.