Eustace Tilley is a caricature that appeared on the cover of the first issue of The New Yorker in 1925 and has appeared on the cover in various forms of every anniversary issue of the magazine except 2017. He was not initially named, but acquired the name from Corey Ford in subsequent issues as part of a fictional magazine history backstory included to fill the early issues of the magazine. The original cover, showing Tilley examining a butterfly through his monocle, was drawn by Rea Irvin, but a younger and more modern-looking version of him as drawn by Johan Bull in subsequent months appeared throughout the magazine in its early years. This later version was given the name Tilley and subsequently the original cover was also declared to be Tilley. Because of the cover's prominence, almost all of the references to Tilley in the press discuss the Irvin version.
Irvin drew three versions of the masthead artwork that featured Tilley in 1925 and 1926. Irvin's third version from 1926 was not updated or revamped until the May 22, 2017, issue with artwork by Christoph Niemann. In 2023, Niemann drew a robot named Till-E for the magazine.
Until 1994, the original cover artwork was reproduced for the annual anniversary edition, but, since then, there has been significant variation in how his character has been embodied. He has become the mascot of the magazine and is described as a dandy. There have been two years without any anniversary issue and in other years, when the anniversary celebration/remembrance has broken from previously-established tradition, it has resulted in stories in publications such as The Washington Post and The New York Times. Since 2008, artists have competed in an annual Eustace Tilley contest with prizes that include the potential to have their artistic interpretation submissions chosen for the anniversary cover. All contest submissions are derived from Irvin's version.