Approximately 200 years ago, the Somnambulist raised Satan in Jericho, Nevada. Satan slew 400 of the 500 residents and wrote a book with the bodies: one sentence inside the skull of each victim.
Eventually, the Sorcerer Supreme Yao arrived, banished Satan back to Hell, and slew the Somnambulist. The Somnambulist was sent to Hell as well. Eventually, he sought to recover Satan's literary effort, but found that a monastery had been built on that site in Jericho, preventing his access.
Stephen Loss visited the Jericho Monastery, and (apparently) unwittingly left behind a page from one of his arcane texts.
Ervil Allred, a serial killer hiding out as one of the monks of Jericho, found the page left behind by Loss. Allred accessed the power in the page to slay several other monks and eventually to summon the Somnambulist. The demon promised Allred great power and the ability to kill anyone he wanted if he would help him regain access to Jericho and Satan's "book." The Somnambulist granted Allred power by having him consume a host, the flesh of the devil (actually the Somnambulist's own heart--an obscure, but potent piece of magic). Allred slew the rest of the monks, deconsecrated the church and then read the Somnambulist's spell, raising the corpses buried in the catacombs below the monastery.
Having recovered the "book", the Somnambulist was now freed from Satan's slavery, and planned to take his first step towards promotion, claiming his first soul when Allred died (and regaining his heart in the process). However, Hellstorm showed up rammed his trident into Allred's abdomen, causing him to disgorge the ingested heart, which Hellstorm then incinerated--destroying the Somnambulist and depriving him of his intended soul.