In the mid 1960s, a bunch of rock and roll bands discovered free jazz, and their minds were blown. The resulting explosion would lead to psychedelic and progressive rock, as seen in bands like The Byrds, King Crimson, and The Beatles, among others.
In the 90s, a similar movement happened with hardcore and punk bands experiencing similar mind-blowing revelations. Themselves inspired by jazz, Krautrock, and proto-post rock like Talk Talk or Bark Psychosis, they twisted the crashing catharsis of their native genres into what would be known as math rock (which is very different from the twinkly finger tapping that is called math rock today).
The most noted example of this shift is post-hardcore outfit Slint’s 1991 album Spiderland. But that album (or the mixture of influences that created it) was the forerunner of a much larger scene. And after Slint’s dissolution, June of 44 may have been one of the most respectable standard bearers for the movement.