Abstract
In this talk, I will begin by sketching out the highly accurate numerical methods that allow us to study axially symmetric, stationary spacetimes containing a Black Hole surrounded by a fluid ring. A definition of mass and angular momentum is introduced for each of the two objects. I then discuss the strong influence of matter on the properties of the Black Hole, including the fact that the ratio of the absolute value of the Black Hole's angular momentum to the square of its mass can exceed ten thousand (|J| /M2 > 104).