The planet Tharn first appeared in Legion of Super-Heroes vol. 4 #3 (January 1990), and was created by Keith Giffen and Al Gordon.
The planet was inhabited by mostly sorcerers who had survived from the planet Zerox, including Mordru. The Khund attacked a defenseless Tharn, with the inhabitants resorting to restoring Mordru's power to save them. Mordru then made himself Emperor and later came into conflict with the Legion of Superheros when holding a Green Lantern (Ron Vidar) hostage.
The planet also made a brief cameo in The Sandman: Overture #3.