The first major use of the word "Antifa" in modern times (that I can find) is something on Breitbart from 4/21/2017, claiming that the mayor of Berkeley was a member of an anti-fascist group 'By Any Means Necessary'. This was significant, because up to that point, the 4/15/2017 protest of Breitbart columnist Milo Yiannopoulos was just said to be comprised of 'multiple liberal groups', which is no big surprise in a town like Berkeley.
The first documented use of 'alt-left' in modern times was when Trump used it in his famous 'both sides' speech following the Charlotteville protest.
After that, use of the word Antifa blew through the roof, and this bogeyman has been used by the alt-Right to justify their actions ever since.
My question is, is Antifa (under that name) documented to exist as an organized group at any point between 2000 and 2017? Was this bogeyman created by Breitbart to have a documented foe against which they could rally? Or has a group large enough to pose a threat to the alt-right existed in the background for decades, only now driven to the forefront?