Who are the 'incels' and how do they relate to Toronto van attack?

Suspect appears to have links to misogynistic online community for the 'involuntarily celibate'

Hours before the Toronto van attack, a post on the Facebook profile of the chief suspect declared that "the incel rebellion has already begun, we will overthrow all the Chads and Stacys".

The message has brought new-found attention to the so-called incel movement, one of the stranger offshoots of the "alt right", and led to calls for the attack to be recognised as an act of far-right terrorism.