Adam was a self-proclaimed follower of Lucifer.
Background
In 2016, Adam purchased a summoning spell and a fossilized feather online in hopes of contacting Lucifer. He claimed the summoning spell was "Satanist Society of America-approved" while the feather had been excavated from one of Lucifer's crypts by the seller.
He convinced his friend Gordy to perform the summoning with him, however, Gordy found the incantation to be ridiculous and could not resist the urge to laugh. He also believed the feather was a fake.
To the misfortune of both, the feather was real, and Lucifer was drawn to it. Lucifer hoped to restore his vessel, which was close to completely rotting away, by using the feather. Lucifer immediately snapped Gordy's neck upon arrival, and took the feather from Adam and used it to restore his vessel, albeit temporarily.
Lucifer expressed dissatisfaction with Adam and Gordy, who were apparently his modern day followers on Earth. Adam was more surprised by Lucifer's vessel however, since it was the rock star Vince Vincente, whom Adam's mother was a fan. Adam revealed that Vince was famous, but was killed immediately after by Lucifer.
It was Adam's declaration that Vince was famous which drove Lucifer to use this fame in a mass-killing spree in Los Angeles.