Ivo Shandor, a physician and an architect of some renown during the early 20th century with a penchant for performing macabre surgeries, is mentioned in the first film and features in the 2009 video game. He is also a relative of Wolf Van Shandor, a famous artist who made mythological artworks.
Having extensive knowledge on the occult and science, his expertise in parapsychology rivals Egon Spengler and Ray Stantz's. Being insane and having a god complex, Shandor deemed that humanity is beyond redemption after the First World War. He established a cult of Gozer Worshippers with close to a thousand followers including Edmund Hoover, Cornelius Wellesly, and Evelyn Lewis, which later, after they died, turned into demonic deities Azetlor the Destroyer, the Chairman, and the Spider-Witch respectively, on June 6th, 1920 with his ancestral island home on the Hudson River as the center of it, dedicated to bringing about the apocalypse. Shandor's cult then researched closely on the paranormal, especially eschatology and ectoplasm. Using his connections to Cornelius Wellesly, who was the chairman of International Steel, Shandor designed 550 Central Park West (55 Central Park West) and his own architectural firm to summon Gozer to fulfill their cataclysmal schemes. Other necessary materials for the apartment building's arcane construction were obtained by Shandor when a mining operation was established in Summerville, Oklahoma in 1927. John H. Tobin, author of several reference books, infiltrated in Shandor's cult to research their methods and history, eventually he published his findings titled Tobin's Spirit Guide.
Shandor also developed a mandala across the city, with the New York Public Library, the Museum of Natural History, the Sedgewick Hotel, and Shandor Island (before it sank) as key nodes protected by horrific creatures that once were his human followers and a captured sloar, demonic creature from Hell that imprisoned within a dimensional pocket inside Shandor's castle, generates a steady stream of black slime used to power the Mandala system and Shandor's island lab and it flows into a series of abandoned city subway tunnels, turning New York City a hot spot for supernatural activity.
After Shandor died, he was interred by his cultists in melodramatic manner: after hours of rituals his body buried in a mausoleum owned by his cult located where Central Park is now; Shandor's grave, in time, like most of other deceased New Yorkers', had desecrated and his remains then scattered. Apparently having no living relatives (revealed later that he does has descendants including Dr. Ilyssa Selwyn), his fortune and resources then managed by a foundation under his name.
Shandor's original scheme comes to fruition during the events of the first film in the 1980s, when the sufficient energy collected causes Gozer's minions to physically manifest in preparation for their master's coming. The Ghostbusters foil Gozer's entry and neutralize it. As revealed in the video game, Shandor is also indirectly responsible for the events of Ghostbusters II, as the psychomagnotheric "mood" slime produced on his island discovered by the malevolent spirit of Vigo the Carpathian underneath the Manhattan Museum of Art; he used Shandor's substance to strengthen himself and to pursue his own apocalyptic agendas after his cursed painting's arrival at the museum.
After decades of operating behind-the-scenes, Shandor finally makes an appearance in Ghostbusters: The Video Game as a main antagonist of the game. It is revealed that prior to his death he made pacts with the Gozarian pantheon, allowing his spirit to become a powerful deity in exchange for his services. By 1991, Shandor possesses the body of Mayor Jack Mulligan and makes Peck head of PCOC to hinder the Ghostbusters, while he uses his descendant – Dr. Ilyssa Selwyn – to invoke the nodes of his mandala and revive Gozer's Mr. Stay Puft Marshmallow Man Destructor form. However, this time, the Marshmallow Man was much weaker and again defeated by the Ghostbusters and failed to capture Ilyssa. Frustrated with Gozer's failures, Shandor decides to use the mandala to merge the ghost world with the human world to initiate his apocalyptic schemes and fights the Ghostbusters himself. Declaring himself "The Architect," Shandor took on the form like a massive demon covered in molten rock. Having underestimated the Ghostbusters, Shandor is defeated after they cross their proton streams during the fight after following him into the ghost world. Prior to the final battle, his skull was found at Central Park by the Ghostbusters as one of their collection of cursed artifacts.
Further details of Shandor's conspiracy will be revealed in the 2021 film Ghostbusters: Afterlife.
The Ghostbusters script lists the spelling of the surname as Sandor, which is pronounced "shandor" and in fact is spelled Šandor as a moderately common Croatian surname.