Karras was the head of the Mechanist Order. He was a brilliant inventor, sociopath, genius, and prophet. He split from the Hammerite organization to found his own faction, due to extremist beliefs, namely that all organic life was inherently flawed. Though Karras suffered from an extreme speech impediment, he was very charismatic and commanded a loyal army of Mechanist followers.
Karras planned to eliminate all organic life in The City, and to do so, he offered the nobility gifts, namely his inventions called Masked Servants. They were in actuality made from the City's street criminals using enslavement masked found in The Lost City.
When Garrett lost his eye to the Trickster, Karras was the one who designed the Mechanical Eye given to Garrett.