Robert Aloysius Crowley  (1791 - 1901  & 2005 - 2007) was a 19th century mystic and a 21st century headmaster. He called himself the "wickedest man in all London" . He first appeared in Scary Go Round in Chapter 16, in which Amy Chilton and Shelley Winters stole a Teapot That Reverses Time from Tim Jones and travelled back to the year 1840. After getting note of their arrival, Crowley concluded that this must be the fulfillment of a prophecy , and thought up a scheme to catch the two women. However, this timeline was undone due to an intervention by Tim upon discovering the treacherous time travel teapot thievery.
Crowley's next appearance in the comic came about due to staff members of Griswald's Grammar School performing (and screwing up) a satanic ritual, summoning Crowley in the process . Crowley thus became the headmaster of the school, but soon developed a severe discontent with the fact that he was magically bound to the school grounds, unable to "go about [his] legendary wickedness" . The Devil paid him a visit, and offered him a deal: Rulership over Britain in exchange for helping Satan to build a demon portal that opens a gate to Hell. The catch: Crowley was contractually obliged to take a wife . First picking out Esther DeGroot, he eventually settled for Erin Winters. (This marriage was later annulled via cell phone text message by Erin's sister Shelley though.) Then Crowley (along with Erin) got sucked into the very demon portal he helped to build . To make matters worse, he was eaten by a demon soon after his arrival in Hell .
Bob is almost certainly an allusion to the real life occultist Aleister Crowley.