Normally in a BDSM relationship.
A person, of either sex, who essentially "controls" the other people (as in plural, generally threesomes) in the relationship.
Is by far the most dominant, and strives to provide the most
pleasure to people under him/her, most of the time without seeking retribution (without getting any
pleasure back).
There can be a Dominant under his/her control, but they
must still be pliant to the Controller's demands.
"She would be such a Controller, I mean, have you seen the
way she behaves?"
"My Controller
really did let us do some really naughty things last
night."