Before he was plucked from Tivoli and deposited in a hellish "hotel", Gibbis worked in town planning. He was engaged in a project to line all his planet's highways with trees so invading armies could march in the shade.
He effectively screwed up the Doctor's only chance to get information out of the Minotaur by letting Howie Spragg go free and be killed. The others grew annoyed with his cowardly behavior and interacted with him very rarely.
Like all of his species, Gibbis was a coward. The Eleventh Doctor described it as an aggressive sort of timidity. Gibbis was happy to sacrifice Howie Spragg in the name of self-preservation and showed a sadistic pleasure in unnerving Amy when he suggested she might have not yet have entered 'her room'. His biggest fear was the Weeping Angels, as they were creatures who wanted to kill rather than opress or enslave him. (TV: The God Complex)