Short answers, pulled from the story.
Alonso Fernández de Avellaneda published his unauthorized sequel to Miguel de Cervantes's Don Quixote in 1614. This work appeared decades before modern copyright laws existed to distinguish between authorized and amateur works.
Women comprised 90% of Star Trek fan fiction authors by 1973 according to scholarly studies. This demographic shift established a predominantly female authorship culture that would influence decades of future fan writing practices.
FanFiction.Net launched on the 22nd of May 1998 allowing anyone to upload content across any fandom without requiring insider knowledge to join. By one estimate fan fiction comprises one-third of all book-related content available online today.
Amazon shut down Kindle Worlds in August 2018 after restrictions on content copyright violations poor document formatting and misleading titles proved problematic. The platform had allowed fan fiction of certain licensed media properties to be sold directly through the Kindle Store until its closure.
J.K. Rowling expressed being flattered by nearly 750,000 Harry Potter fan stories existing online by 2014 ranging from short stories to novel-length tomes. These works included various formats from short stories to novel-length tomes created by fans.