According to the Season 2 DVD commentary, Soul-Bot was originally created to look after the children on Astrobase Go!, which was originally intended to be a futuristic school/space station orbiting the moon. Soul-Bot is powered by love which it filters from the air and stores in its chest cavity.
Since Publick and Hammer have taken over the Astrobase, Soul-Bot was re-purposed into a therapist, painter's model for Doc Hammer, and occasional guitar player for duets. Soul-Bot is credited with HELPeR's voice in the credits.
In reality, Soul-Bot's voice work is actually Jackson Publick doing a robot impression, which is then processed through audio filters by Hammer to make it sound more mechanical. Reportedly, after his first few appearances, HELPeR's voice sounds are simply reused over and over.