Programmer Dave Durran had worked at Mattel Electronics on the hardware designs of the Intellivision Master and Keyboard Components and Intellivoice before leaving to join the startup Imagic. At Imagic he wrote much of the system code used in game development and worked on the hardware design of the Imagic cartridge ROMs. He also wrote the sound effects for the games.
With everything else he was working on, he says that writing Fathom was a "kind of afterthought." It was designed to be a children's game with (mostly) friendly characters and an easily understood goal. The theme is the same as Imagic's Atari 2600 Fathom designed by Rob Fulop, but the gameplay is slightly different.
Imagic later released a version of Fathom for Colecovision
EXPERTS CLUB PERFORMANCE STANDARD: Fathom was released after the final Numb Thumb newsletter, so no performance standard was published for the game.