WordPress comes with a default theme to display the front-end of the website. This is the first theme that you see when you first install WordPress. The user can then replace it with any other WordPress theme.
The default WordPress theme is used to showcase the features of WordPress, so it is usually feature rich and can be used to create most basic websites. The default theme also serves the purpose of a fallback theme. In case a user’s installed WordPress theme gets deleted or something goes wrong, then WordPress automatically falls back to the default theme.
The first WordPress theme was created by Matt Mullenweg when WordPress was released in 2003. At this time users didn’t have the ability to switch themes yet. After the original theme, came the WordPress Classic Theme with WordPress 1.2. It wasn’t until the Kubrick theme was released with WordPress 1.5 that users were given the ability to switch themes. Although many users changed their themes, Kubrick remained the default WordPress theme until it was replaced by TwentyTen in WordPress 3.0.
Every year since 2010 the team behind WordPress comes out with a new default theme that is named after the year. TwentyTen is still one of the most popular themes in terms of total downloads.