Gibbis

Gibbis was a native of Tivoli, a green planet whose residents took a strange delight in being subjugated.

Biography
Gibbis' old school motto was "Resistance is Exhausting."

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 behaviour and interacted with him very rarely. After his escape from the hotel, Gibbis requested the Doctor drop him off in his TARDIS at the nearest galaxy. (TV: The God Complex)

After meeting Albar Prentis, the Twelfth Doctor referred to his meeting with Gibbis and how as a result, he didn't like the Tivolians. (TV: Before the Flood)

Personality
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. (TV: The God Complex)

Behind the scenes
According to The Brilliant Book 2012, a book that contains non-narrative based information, the reason Gibbis feared the Weeping Angels was they had no interest in conquest, only killing.