PHP was created by a man named Rasmus Lerdorf, who was writing Common Gateway Interfaces in C to maintain his personal homepage. He then got these CGIs to work with web forms and databases, and called it 'Personal Home Page Forms Interpreter', PHP.
PHP was meant for the web environment. While originally just used to maintain Lerdorf's homepage, it has now completely evolved into it's own language that is maintained by a group of developers simply known as The PHP Group.
Because PHP can be used with just about anything related to web development, like HTML, Databases, and graphics, It is commonly used on a lot of websites, like Facebook, Wikipedia, Whatsapp, Wordpress and more. According to W3techs, of the sites that share the languages they use, PHP is used in 77.8% of them!
PHP was created by Rasmus Lerdorf to improve and maintain his homepage. This quickly turned itself into a programming language of it's own, that is now widely used across the internet and is maintained by a group of developers. It is also incredibly common across the internet because it is a general purpose language, and can be used for just about anything related to the web.