Sourdough is pretty much an average cheese, lettuce, and ham sandwich, with the two olives on it acting like its eyes. Its true form is that of an amorphous and glowing purple entity outwardly resembling some sort of slug/dragon hybrid.
Emperor Awesome tried to flirt with Sourdough but got blasted by one of Sourdough's guards.
Wander, Sylvia, Lord Hater and Commander Peepers
Originally in its original form, Sourdough seemed fond of Wander due to his position as most wanted in the galaxy and seemed mainly indifferent to Sylvia, Peepers, and Hater (although later he did become impressed with Hater's power), however after Wander saved Lord Hater from being possessed by Sourdough, it began searching after the four, but mostly the latter two in hopes of getting revenge. In "The Axe", it's shown that he doesn't really think highly of Lord Hater as a villain but instead as a "ne'er do well". It also shows that he has some respect for Peepers saying that Peepers actually knows what evil is all about, unlike Hater.