Controller

[Sarah]

Something used to control things

[Cami]

A person or thing that directs or regulates something.

[Rihanna]

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 [Controllers] demands.

[Mark Zuckerberg]

A device used to play video games, or a person [in control] of a [machine], aka [a train]

[Jason Yan]

Contextually can refer to a [remote control] or a [device] used for [gaming].

[Renato]

Controller in Table Tennis. A stroke enabling the opposing player to perform set exercises or practices.