Pop culture characters such as Dracula and the Frankenstein Monster exist in the Marvel Universe. This is usually justified as a second-hand account of events as told to credited authors Bram Stoker and Mary Shelley, although the general public continues to believe them to be fictional. Robert E. Howard's Conan the Barbarian, Red Sonja, Kull the Conqueror, and Solomon Kane also have real-life existences in the Marvel Universe. The Hyborian Era of Conan and Kull is considered part of Earth-616 pre-recorded history. However, they rarely encounter modern Marvel superhero characters. This is most likely possible due to the uncertain legal status of Howard's works before 2006 when they became public domain. As of 2019, Conan the Barbarian, as well as Kull the Conqueror and Solomon Kane, have been firmly integrated, thanks to Marvel regaining the publishing rights to the characters. Other licensed works that have been incorporated into the Marvel Universe include Godzilla, the Transformers, the film "" (in the character of Machine Man), Rom the Spaceknight, the Micronauts, and the Shogun Warriors. In most cases, such material is either restricted from use after the license expires or the characters redesigned or renamed to avoid copyright infringement.