Since its destruction, many have sought to own pieces of the fabled Star Forge‒an automated Rakata shipyard capable of infinite manufacturing. A Selkath experimenting with cybernetic applications using Rakatan technology was one of those looking to harness the Star Forge's immeasurable power. With the shipyard's self-replicating properties, the Selkath theorized implementation of its parts could allow his test subjects to survive the grafting process, and to achieve virtual immortality. When the Order of Revan made a piece of the Star Forge available to him, the Selkath was able to prove his theories and the Infinite Army was born.
This is not the first time the notion of an Infinite Army was conceived. A tormented Jedi looking to destroy the Sith Emperor once appropriated a long-abandoned Rakata foundry built into an asteroid. However, his reputed plan to use the foundry to build an “infinite army” of extermination droids was ultimately prevented.