Vrumpus was and probably still is Lumi the Snow Queen's most loyal servant and caretaker. He was first mentioned in the Jack of Hearts arc, when Jack recalls meeting her. He served the Snow Queen when she was still innocent and still very much loved by her people. He allowed Jack to work for them, due to Lumi enjoying his stories. But he gave Jack the job of janitory duties, cleaning the stables, latrines, and such. Eventually, Jack would weasel his way into Lumi's bed. As such, Vrumpus, despite his distrust of Jack, treated him to the better rooms and lifestyle; as was customary for Lumi's lovers.
Jack left her side, when she became ill, and naively gave him her powers. While Vrumpus tended to his ill lady, Jack abused his powers and tried getting into bed with every lovely lady in Lumi's kingdoms; she passed as she represented winter. Eventualy, due to Jack's abuse of her powers, the people began to blame Lumi and planned to revolt against her. When he warned her, she was shocked to know this, as she had thought they still adored her. Eventually after her loud tongue lashing at the peasants, Vrumpus pointed out a clue to Lumi's illness that it came in the mornings. When she answered yes, he pointed out that she wasn't ill. Lumi was pregnant and judging by the timing, it was Jack's.
To protect her, Vrumpus helped her escape the castle and reside with her sister Kesa. A year had passed and Lumi gave birth to her son, but Jack never returned with her powers as he promised. This turned his lady cold and cruel as the winter she represented. But despite her change, Vrumpus was still loyal to her. Although both probably hated Jack for his deception, Vrumpus did find her newborn son adorable. Lumi did warn him though never to mention his father's name to her ever again.
As the years past and Lumi rose in power, Vrumpus was left to take care of her son Evelyn-Lawrence-Pinder-Shinks-Cobblepewter. The boy was rather sickly and Vrumpus took great care of keeping him safe. When the Snow Queen fell under Briar Rose's sleeping spell, her powers transferred to her son, who called himself Jack Frost II. Despite how he felt angered by not knowing his father, Jack felt no ill will towards his mother or Vrumpus. In fact, on his search to find his father, he decided to send recordings to Vrumpus of his journey.