Hypertext Markup Language (HTML) was the first language designed for use presenting data and images across the connected internet. It provided a way to easily distinguish code from data to be presented. It was also much easier to use than previous coding schemes TeX, Scribe, and GML that were used prior to the public internet by the military and universities that worked on and used ARPANet and MILNet.
This made it the language of choice for creating webpages and even today is still the primary language through many of the original tags have been deleted with newer versions, it is still the primary language used to create web pages.