A controller is someone or something that manages, directs, or regulates how things work.

In video games, a controller is the handheld device you grip to play: it has buttons, joysticks, and triggers that let you control characters on screen. The original Nintendo controller had just a directional pad and two buttons, while modern controllers have many different inputs for complex games.

In business, a controller is a senior financial officer who manages a company's accounting and makes sure money is tracked correctly. A financial controller oversees budgets, prepares reports, and ensures the company follows financial rules.

The word also describes people or devices that regulate systems: an air traffic controller guides planes safely through the sky, cruise control controls your car's speed, and a thermostat acts as a temperature controller for your home's heating and cooling.

What all these meanings share is the idea of directing or managing something: making sure it does what it's supposed to do. Whether it's controlling Mario's jumps, controlling a company's finances, or controlling air traffic, a controller helps keep things running smoothly and safely.