Thorn was a red dragon in the Inheritance Cycle by Christopher Paolini. Thorn is very young, younger even than Saphira, and is very inexperienced. His body has magically altered to be much bigger than it should by Galbatorix so that Thorn and his Rider, Murtagh, can be formidable enemies for Eragon and Saphira. Thorn and Murtagh are not in the service of Galbatorix by choice, but were forced to swear oaths of loyalty to him in the "Ancient Language", the language of magic, meaning they cannot break their oath unless their true names change. It was through use of Thorn and Murtagh as his avatars that Galbatorix was able to slay Oromis and Glaedr, leaving Eragon and Saphira as the last free dragon riders in Alagaësia. Durin the battle at Uru'baen, Murtagh was able to change the True Names of Thorn and himself through the former's love for Nasuada. Thorn rebelled alongside Murtagh against Galbatorix and helped Saphira and Arya to kill Shruikan, and after the battle, flies north with Murtagh to cool off and vent all the rage he has built up, and was given a cool if respectable farewell by Glaedr and Umaroth, who decreed them as equals and worthy of being Rider and Dragon. Thorn was noted as having a very musical mental voice by Eragon.
- It is noted that Galbatorix's magic has made Thorn larger than what would be normal for a dragon his age.