Cassie Claire is a Harry Potter BNF turned pro author. She became infamous for plagiarism, grifting off her f-list, and bullying people. Some comprehensive background links:
Her two young adult urban fantasy series are Mortal Instruments and Infernal Devices. The film rights for the Mortal Instruments series were optioned in 2009.
As one of fandom's biggest wank magnets, Claire comes up on f_fa from time to time. In April 2013, Gentlefailers discussed at great length the Mortal Instruments movie trailer. Far down in that thread, one nonny linked to this blogger, who claims that Claire's lawyers "are trying to remove any Internet sites which mention her fanfic plagiarism." Not long after, there was another long thread on Cassandra Clare's Gigantic Tourbus.
After reading The Cassandra Claire Plagiarism Debacle (currently only accessible through the Wayback Machine) a nonny was curious exactly how big/powerful CC was and asked for points of comparison. Meme obliged as best it could, though it was fairly unanimously agreed that no one since has been as influential or widely known.