Deimos was discovered by Hall on august 10 1877.
Phobos was also dicovered by Hall, on august 12 1877.

Phobos is the inner satellite, Deimos the outer. Phobos is very close to Mars. So close even, that in 50 million years, it will either crash onto mars or break up into a ring.

Deimos and Phobos are composed of carbon-rich rock like C-type asteroids and ice. Both are heavily cratered. Deimos and Phobos are probably asteroids perturbed by Jupiter into orbits that allowed them to be captured by Mars. 

Pictures of Deimos

Pictures of Phobos