Great thread!
So, the troll is a shaman and a cannibal. He was pushed out of his homelands, and found himself at odds with the local farming community. After a particularly nasty battle with three of the lead temple priest's sons, the troll was severly wounded by learned of its ability to recover from devastating wounds (it had never been impaled on a pitchfork before). During this battle, one of the sons (the blacksheep of the religious family - a rogue) read a scroll which summoned a hellhound. The hellhound scarred the troll with flames, and was mortally wounded when the troll threw it off a cliff. During the fight, the rogue was also tossed off the cliff, and presumed dead. The other two brothers, one missing an eye, were forced to retreat.
At the bottom of the cliff the troll found the rogue and hellhound barely alive. Though it was dim, the troll realized the rogue might be worth more alive than dead. And though it was mighty hungry, the troll was awed by this mere dog which had left it scarred for life. So the troll nursed the hellhound back to life (though it walks with a limp and lost ability to breathe fire) and it has a cold truce with the troll. The rogue, on the other hand, suffered a broken back and cannot move - the troll dragged him back to its riverside cave to interrogate him. The troll installed the shards of glass originally to keep the rogue from dragging himself to the river, but now the troll simply likes the sparkling effect. The troll brings scraps of food for the rogue, keeping him alive with the promise of returning him to his brothers, in exchange for details on the temple. The troll has become enamored of the idea of religion and trys (unsuccessfully) to mimic the rituals as the rogue describes to him. Both of the rogue's brothers are terrified after their last fight and presume their brother to be dead -- they won't even think about hunting the troll.