In the 1920's, Dr. Porstmann of Germany published a document proposing a standard for paper which would later change the world. Dr. Porstmann's theory quickly became DIN approved, which is a standard in Germany meaning 'Deutsches Institut für Normung'. In English, DIN translates as 'German Institute for Standardization'.
A4 became a standard in the late 1970's. However, even though the standards were introduced in the early 20th century, it took more than 50 years for the standard to be recognized worldwide.