Could be Cain has something over him to make Deimos follow his orders... Either way he does that bastard's dirty work...
Deimos is a fighter assigned to the starfighter Equinox. He is close to Cain and a confidant of The Shady Plan, but the exact nature of their relationship has not been revealed. He is known for his almost perpetual silence.
Like Cain, Deimos is from the part of the colonies where there is a large population of Russian descent.
While Deimos is very reluctant to speak, HamletMachine has confirmed that there is not a physical issue with his voice.
He is most likely named after Deimos, one of the planet Mars' two moons, the other being Phobos. In Greek mythology, Deimos and Phobos were twin brothers who represented Terror and Horror respectively.
In an early sketch, Deimos was portrayed with an array of scars on his arm and shoulder. However, HamletMachine has clarified that in canon, Deimos does not have these scars.. It has later been proven he does not have these scars by playing Starfighter: Eclipse and persuing him, to get his picture set there are clearly no scars visible on his body, in the Cargo holder scene, or the scene with Cain in the medical bay.
Deimos speaks more with his body language.
He tried to court Cain thinking Cain was interested in him. Cain personally asked Deimos to stalk his navigators.
As of the update Deimos will most likely end his partnership with Cain.
Deimos proved to be dangerous from the very beginning, when Cain came across Deimos stabbing another man in the shoulder.