The phrase "titular monster" refers to a main or prominent monster character in a book, movie, or other storytelling medium. It emphasizes that the monster is the central focus or title character of the story. Full definition
This time, The Grinch is being produced by the same studio that makes Despicable Me, and the titular monster is being voiced by Benedict Cumberbatch. (relevantmagazine.com)
This animated prequel to the 2004 summer blockbuster Van Helsing finds the titular monster hunter heading to London to try and stop none other than the horrific Dr. Jekyll and Mr. Hyde. (rottentomatoes.com)
As much as its titular monster is an amalgam of different creatures, The Relic is an entertaining mashup of old school monster movie, lashed to the modern interest in gore and savagery. (impulsegamer.com)