True to most incarnations and portrayals of Satan, The Devil, also known as "Lucifer", runs Hell and seeks to cause evil in the world. In the cosmic scheme of things, his presence is required so as to influence evil in order for good choices and morality to have any weight, as demonstrated in one episode. However, his relationship with God is marked by resentment and a desperate need for attention, much like a son and his estranged father. On a few occasions, they have been shown to be relatively affable with one another, even if the Devil becomes frustrated with God's lack of attention and tendency to forget about things like his birthday. Nevertheless, the Devil uses any opportunity he can in order to condemn souls and mess with God's operations.
The Devil is frequently helped in these escapades by his demonic minion, Smeck. True to the tradition of many villainous characters, the Devil regularly abuses Smeck, even for the smallest errors or mistakes. (On one occasion at God's advice, the Devil tries to treat Smeck with kindness and respect, which the demon found creepy and forced due to it not "being his true self".)
God, the Devil, and BobAt the beginning of the series, God expresses his desire to destroy the world and restart after seeing the worst of humanity right up to the then-modern day. Sensing an opportunity to gain more power in a new world that does not anticipate him, as well as reveling in the idea of destruction and sensing a chance to have more relevance in God's life, Lucifer is all onboard with the idea. God, however, has second thoughts, wanting to give humanity a chance. Being a "sporting man" by his own description, God has the Devil select the one who will represent humanity and influence his decision to spare or eradicate it. The Devil selects Bob Allman, a somewhat sleazy and self-absorbed father, seeing it as a cheap win. Bob, however, manages to pull through despite his faults.
In each of the episodes, the Devil attempts to sway Bob in some fashion to screw up God's current mission and damn Bob's soul in the process. Among two of his more despicable acts involved him assuming human disguises, once as the boyfriend of Bob's daughter, Megan, in a plot to harm him as a father, and once as Bob himself while leaving Bob imprisoned in a mental institution. In the latter case, he manipulated Bob into getting arrested and institutionalized by means of a "homunculus", a small replica of Bob he used to force Bob to punch out a cop. During his time as "Bob", the Devil fell for Bob's wife, Donna, due to her caring attention while he was sick. He was foiled by Bob's timely arrival. Despite telling Bob to take care of Donna, the Devil later left his palm pilot with the next day's sporting event scores to get the two hooked on gambling, culminating with Donna almost losing her soul to the Devil in the process.