From Wikipedia
Gauntlet Legends is an arcade game released in 1998 by Atari Games. It is a fantasy themed hack and slash game, a sequel to 1985's popular Gauntlet and 1986's Gauntlet II. Its unusual features for an arcade game included passwords and characters that could be saved, enabling players to play over the course of a long period of time.
Story
In ages past, a corrupt mage named Garm used a set of Runestones to summon a demon named Skorne (It is not stated what Garm intended to use Skorne for; however, as Gauntlet Legends introduces Garm as a "greedy young mage", it can be assumed he wanted Skorne for his own personal gain.) However, Skorne crushed Garm and imprisoned his soul in the Underworld. Skorne, fearing the power of the Runestones, scattered them throughout the four realms, so that they could never be used against him. The player(s) must defeat the end bosses of each of the four realms to obtain the four golden keys which allow access to Skorne's temple. While traveling through each realm, he/she/they must also collect the Thirteen Runestones from where they have been scattered. The complete set of Runestones allows him/her/them to pursue Skorne to the Underworld in order to finally destroy him. The players must find 3 rune stones on each kingdom in order to defeat Skorne in the Underworld, and of course 1 from the battle grounds.