It is claimed to have been invented in 2007, although Plato may have made an early version of it thousands of years earlier. In his Republic, the main character is Socrates, who was actually his teacher. The other characters are Socrates's students, and the work is a dialogue between all of them. So, Plato was involved in creating a dialogue, but he was basically just copying Socrates. An alternative theory is that it's just a fanfiction, which would actually make it a prototype of UnAnything Wiki. The writing style, but not the format or genre, supports the latter hypothesis.
Tumblr was founded and launched on February 2006 by its developer, Marco Arment. Before the current state of this godforsaken website, Tumblr was actually really good. People discussed about various issues and topics in a civilized manner. All was good until one day, on circa 2012, special snowflakes started to take refuge on the site.
2012 was the year where Tumblr went downhill. Various sub-humans flooded the site, turning it into a cesspool. The sudden increase of furries, weebs, etc is one of the contributing factors of what ruined this website.
This is it. This is the year where Tumblr died. SJWs, feminazis, and people with gender dysphoria completely conquered the site turning Tumblr into a hugbox and a "safe-space" for people with mental disabilities.
2018 marks the removal of any sexually-explicit content on Tumblr, removing the only good thing left from this website. This event caused mass-panic among the users of this platform. Good night, sweet prince.