It was introduced in 1996 and its popularity exploded from there and has remained one of the most used ever since.
Apache to a server is what Microsoft Windows is to a PC. A base built server or PC can not function without the software that runs it.
A majority of websites today are using Apache and Apache was the first to serve 100 million websites in 2009.
This is an amazing feat for a well-engineered and respected server software.