A human paladin of Pelor, Egon Sonnen was the hero who banished Shardmoon Castle. However, due to the schemes of Raziela the Shroud and the true nature of the Iridescent Blade, his heroic actions had unexpected consequences.
The residents of that dark keep soon saw to it that the Paladin’s soul was locked away in some sort of ghost jail.
His recounting of his tale helped them to begin to unravel the twisted schemes engineered by Raziela the Shroud. When Iris Four sought to freeze the denizens of Shardmoon Castle in time and seize control, Egon was able to escape.
Once free, he arrived just in time to blow Raziela’s cover when she arrived on the island.
Egon Sonnen pretty much means ‘sword’ and ‘sun’, which seemed appropriate. It’s a bonus bit of pop-culture irony that a guy named Egon wound up in a ghost trap/containment unit.