Salesforce controllers, also known as Visualforce controllers, are used to execute a set of instructions. Controllers specify what happens when a user interacts with the Visualforce Markup components such as Visualforce tags, HTML, fields, etc. When a user clicks on a button or link on a Visualforce page, the associated controllers will display the data related to the user action or component. The controllers have the ability to modify component behavior. They work on an MVC(Model-View-Controller) approach. Salesforce provides the below types of controllers.
Standard controllers
Standard List Controllers
Custom Controllers