Ser Mettin is one of Kirkwall's Templars.
Involvement
If Hawke sided with Meredtih during Showdown at the start of act 3, Ser Mettin is encountered during the quest The Last Holdouts.
Ser Mettin and Ser Agatha enlist the aid of Hawke in dealing with citizens harbouring apostates. Unlike Ser Agatha, he holds extreme views about his duties. If Hawke chooses to side with Agatha regarding on how to deal with the mage sympathizers, or attempts to remain neutral, Hawke will be forced to kill Mettin. Otherwise, Hawke will fight Agatha alongside Ser Mettin.
If Hawke sided with Orsino during Showdown at the start of act 3, Ser Mettin is encountered in the quest A Noble Agenda.
Ser Mettin leads a squad of Templars to interrogate a mage sympathizer in Lowtown. He is then interrupted by Hawke and orders the Templars to attack Hawke and their companions and is slain in the conflict.