Pickwick is the name of one of the ghosts in the Haunted Mansion.
Pickwick was a plump man likely during the Victorian era or maybe Edwardian Era. At some point in time he died and for unknown reasons became a ghost. His undead spirit would go on the haunt the Haunted Mansion where he enjoyed parties in the Grand Hall of the manor. It is unknown if he had any relation with the mansion in life or simply moved there post-mortem.
He is identified by his Dickensian wardrobe including a vibrant red coat and red scarf. He is also noted for his jovial spirit despite his large physique and short stature.
Pickwick was one of the only two characters actually named by the imagineers and writers behind the Haunted Mansion in the original 1969 script; the other being Madame Leota. His name is believed to be an inside joke regarding the Pickwick Center of Glendale, California, this centre being a location which imagineers had to pass by on their route to work.
The appearance of Pickwick's character is inspired by the character of Samuel Pickwick from Charles Dickens' 1836 novel The Pickwick Papers (the first novel he ever wrote). Samuel Pickwick was an overweight gentleman who founded a club called the Pickwick Club, a group in-which members were called Pickwickians. It is believed this Pickwick's character was based on historic businessman Eleazer Pickwick (c.1749–1837) who was incredibly rich and founded the Somerset Coal Canal.
Due to Charles Dickens, Pickwickian Syndrome became the nickname for obesity hypoventilation syndrome (OHS) which causes severely overweight people to fail to breathe consistently/deeply enough, sometimes resulting in death. It is possible that this could have been the ghost Pickwick's cause of death given his appearance and love for hyper activity.
The Haunted Mansion
In the Haunted Mansion, Pickwick can be seen in the ballroom scene where he dangles from the chandelier through the use of a hooked cane. In one hand he holds a glass of ghostly red wine which he is shown to be enjoying with an ancient Roman soldier and ancient Egyptian woman.
A ghost modelled after Pickwick appears in the graveyard scene of this film with the credits identifying him as the, "Happy Ghost".
In this comic-book series, Pickwick is named to Erasmus Cromwell Pickwick. He is identified as having been a, "Mole Burglar" who suffered from a severe fear of heights. He attempted to break into Gracey Manor to try and find the treasure of Captain Blood only to die of a panic-attack in the Stretching Room.
In Disney Kingdoms: The Haunted Mansion, Pickwick is identified as one of the ghosts who moved to the Haunted Mansion for post-mortem retirement. However he became trapped in the mansion due to the cursed fog summoned by the evil pirate ghost known as, "The Captain". He becomes a sort of guide to the mansion's ongoings to the protagonist Danny Crowe and even aids Danny in his fight against the Captain by assembling the mansion's ghosts to attack the pirate.