Dominant
From BDSM Wiki
A Dominant is the person in charge of a power exchange relationship who practices some form of domination, or the term could be used to describe someone with a series of dominant personality traits.
It should be noted that in general usage, the word Dom is a short, gender non-specific replacement for the word Dominant. "Domme" (usually pronounced "dough-may") has come to indicate a female Dominant.