A book "Design Patterns: Elements of Reusable Object-Oriented Software" written by four authors in which 23 design pattern explained in three categories 1.) Creational Design Patterns 2.) Structural Design Patterns and 3.) Behavioral Design Patterns. Four authors of this book known as "Gang Of Four".

The authors of the DesignPatternsBook came to be known as the "Gang of Four." The name of the book is "Design Patterns: Elements of Reusable Object-Oriented Software" ."Gang of four" is short name of this book.You can search "GOF" also on net.