Is known in battle as "Constaint Splinterblade" up until you face him as a complete Paladin in This Little Sword of Mine, where he is known as "Constaint Solidblade"
This NPC is found in multiple locations. The map below shows where the NPC is first encountered.
Constaint as a Paladin
Constaint during the quest This Little Sword of Mine
Constaint during Big Sollerets to Fill