From his introduction onwards, Horribus is depicted as possessing only middling intelligence but strong leadership skills - he is extremely self-confident, decisive, charismatic and fully capable of maintaining discipline among his followers. He relies on the advice of Psyk, who he obviously recognises as the brains of the dimension but sees as a geek. Horribus is impatient, touchy, prone to fits of fury and has little or no sense of humour. A softer side (played for laughs) is hinted at in references to a soft toy collection. Horribus' arrogance and sense of his own position are in marked contrast to his grovelling behaviour towards his own boss, the Demon King, to whom he appears to be very loyal.
Character arc Edit
Flashbacks during Torg's sojourn in the Dimension of Lame showed that before elevation to leadership, Horb was an efficient, keen and ambitious demon, and close friends with Psyk, Reakk, Isp and Osp. His focus on the job at hand and loyalty to the mission were rewarded when he was made into the new demon lord despite his flaws. The promotion changed Horb's name to Horribus, and gave him aristocracy along with his linage: brother Terb/Terribus, sister Plorb/Deplora and baby brother Borborb.
Horribus' reign appears to have included a lot of boredom, however. Once the Elder Villages were conquered, it seems the demons rapidly ran out of souls to torment and were forced to find new ways to torture and kill time instead. Given Horribus' obvious eagerness to prove himself in every endeavour, this must have been a source of some anxiety to him. In this context, it's perhaps understandable that Torg's appearance and subsequent escape made a profound impact on Horribus. He apparently saw Torg's escape as a personal insult and failure and over the years his determination to recapture Torg grew into a deranged obsession that gradually became strongly tinged with paranoid ideas about Torg's malevolence and powers. Each year, at Halloween, he made attempts to recapture Torg by sending demons into Torg's dimension to bring him back. Perhaps the most humiliating point in Horribus' career as demon lord came when Gwynn enslaved him at one Halloween party and used him as a waiter, cleaner and even strobe light.
The final chapter of Horribus' story sees him growing far beyond his original stereotypical character. Pete creates sympathy for Horribus, even as he commits worse and worse acts of viciousness, by charting his descent into madness and the gradual, painful, rupturing of his relationships with the other demons. Our final sight of Horribus is full of pathos - he sits curled pitifully on the Demon King's hand, muttering to himself in a paranoid daze, before being demoted to a normal demon, crushed and thrown broken into one of the deep crevasses of the Dimension of Pain's landscape. Presumably Horribus - now Horb - is still there, and he may yet (here's hoping!) have a role to play in the denouement of Sluggy Freelance.