The authorship of the Commodore 64 titles was at the time even more uncertain. The conversions of existing Spectrum games "Sabre Wulf", "Underwurlde" and "Nightshade" were handled by Firebird, who hired Mr Micro, Softstone, and PSI, respectively, to develop the titles. "Imhotep" was submitted to Ultimate in a virtually complete form by author Manuel Caballero, who had previously written "Batty Builders" and "Firefleet". Ultimate did not make any announcements regarding the authorship of the other Commodore games, but an article by Martyn Carroll revealed how Frank Gasking of "Games that weren't 64" managed to identify the creators as Dave and Robert (Bob) Thomas based on a message that appears on the final screen of "Dragonskulle". These two brothers were also the creators of the previous three games of the series "The Staff of Karnath", "Entombed" and "Blackwyche". In an interview with the brothers in Retro Gamer magazine, they revealed they also authored Outlaws, in just six weeks, so Ultimate would have something for the Commodore 64 for Christmas.