Scarlet Temper is an allusion to the Robin Hood character Will Scarlet. In recent adaptations of the Robin Hood legend (not so much in the traditional tales) Will Scarlet is often depicted as a bit of a hothead with a bit of a ruthless streak. In that respect Scarlet Temper is a bit of a telling name as he can be a choleric.
His elder sister is Lawlex, the headmare of the town guard of Trottingham and it seems that the two of them have fallen out with each other. It may not come as much of a surprise given her being an exemplary official and keeper of the law while Scarlet's Temper has earned him the nickname "Lawless".
That's about all I can say about him at this point without providing any spoilers for the players of my group.
Same as with the other NPC images, there is an alternate version without reduced opacity.