Meredith Stannard is the Knight-Commander of the Templars of Kirkwall and a very influential and powerful woman - however her fanatical hatred and fear of mages serves to turn her into the primary antagonist of Dragon Age II as she leads a terrible crusade against magic that claims many innocent lives and spreads great fear and tyranny across the land.
If players side with Meredith in Act 3, she explains why she views magic the way she does; when Meredith was younger, her sister Amelia developed magical talents but her family decided to shield her from the Chantry, knowing that she couldn't survive in the Circle or pass their rigorous tests. Amelia was described as a kind and gentle soul who was unprepared to carry such a heavy burden and was utterly grateful for her family's efforts. One day, Amelia was possessed by a demon and turned into an abomination which slaughtered her entire family save for Meredith, who survived. The Templars eventually slew her sister, but not before the abomination killed 70 villagers. This traumatic, heartbreaking experience led to Meredith's harsh view on magic and why mages must be treated as people with a curse.
Meredith is somewhat unique in the fact she is the first human in the Dragon Age series who serves as the final boss of a game.
During the final confrontation Meredith is empowered by the same corrupt lyrium that had been causing havoc throughout the game ever since it was discovered during an ill-fated expedition, which caused her inner-hatred for magic as well as her paranoia to take over her and drive her on a murderous rampage in which even her own followers realized her danger and stood against her. She is defeated in combat by Hawke and his/her companions, and then petrified by the lyrium sword after beseeching the Maker for help.