Ella is Christian's mother. In the second movie of the trilogy, Fifty Shades Darker, it is revealed that the women who Christian begins a BDSM relationship with must look like his mother. When explaining this, he refers to himself as a sadist, rather than a Dominant due to the fact that he likes to inflict pain on women who look like his mother as a way to cope with his past.
Christian does not like the name Ella. Lol