Aloysius J. Troll is a surly old magical troll that appeared in the episode "Snappy's Way". He is an old hermit who detests the outdoors and only comes out of his hole beneath Troll River Bridge every 500 years. If somebody catches him, he will grant them one wish.
In "Snappy's Way", Snappy found Aloysius hanging from a tree, having apparently been caught in a trap. When Snappy saved him, Aloysius granted him one wish which was to have grown ups obey him. After granting his wish, Aloysius went back to his hole. Later on, when Snappy began abusing his power, the Smurflings sought out Aloysius and asked him to remove the spell from Snappy. They then forced him to come with them and stop Snappy who had the Smurfs to the mountains where they had been caught in an avalanche due to Snappy's recklessness. After Snappy realized the error of his ways, he used his power to control the grown up Aloysius into helping them save the Smurfs, and after they returned home, Aloysius removed the spell from Snappy and angrily went back to his bridge.