Sir Tim Berners-Lee developed HTML in late 1991 but did not formally release it. HTML 2.0 was released in 1995. HTML 4.01, a significant version, was released in late 1999.
He apparently had been working on this since all the way in 1980 and had a system for his own personal use. Like a lot of things, it wasn’t a stroke of genius in few seconds but rather decades long thinking and mulling over how the linked documents should/can look like.