At its heart, QAnon is a wide-ranging, completely unfounded theory that says that President Trump is waging a secret war against elite Satan-worshipping paedophiles in government, business and the media. QAnon believers have speculated that this fight will lead to a day of reckoning where prominent people such as former presidential candidate Hillary Clinton will be arrested and executed.
That's the basic story, but there are so many offshoots, detours and internal debates that the total list of QAnon claims is enormous - and often contradictory. Adherents draw in news events, historical facts and numerology to develop their own far-fetched conclusions.
Where did it all start? In October 2017, an anonymous user put a series of posts on the message board 4chan. The user signed off as "Q" and claimed to have a level of US security approval known as "Q clearance".
These messages became known as "Q drops" or "breadcrumbs", often written in cryptic language peppered with slogans, pledges and pro-Trump themes. ... social media and opinion polls indicate there are at least hundreds of thousands, if not millions, of people who believe in at least some of the bizarre theories offered up by QAnon.
And its popularity hasn't been diminished by events which would seem to debunk the whole thing. For instance, early Q drops focused on the investigation by special prosecutor Robert Mueller.
QAnon supporters claimed Mr Mueller's inquiry into Russian interference in the 2016 US election was really an elaborate cover story for an investigation into paedophiles. When it concluded with no such bombshell revelation, the attention of the conspiracy theorists drifted elsewhere.
True believers contend deliberate misinformation is sown into Q's messages - in their minds making the conspiracy theory impossible to disprove.