The Gil'Dishpan were members of an alien race of slug-like water-breathing sentient beings who had developed a highly technical society by virtue of their powerful telepathic and telekinetic abilities.
As a whole, the Gil'Dishpan exhibited extreme distate for airbreathing species, considering them inferior to their own race in all ways. Because of their feelings of superiority, they had no moral qualms about conquering and subjugating planets inhabited by airbreathers for their own gain. The only problem they had was maintaining sufficient occupation forces on the conquered worlds, as most Gil'Dishpan had severe qualms about being forced into close contact with beings they considered to be "lesser" than them.
Outside of water, their race was unable to breathe, therefore they wore protective bubbles whenever they were on dry land, which was necessary when dealing with beings who only breathe the atmosphere and not water.