Dumuzid

Dumuzid is one of the main antagonists of the video-game, Catherine. He is an immortal demigod, though his only duties appear to be carrying out Ishtar's will. The player first meets him as Boss, and is later introduced as Thomas Mutton before being finally identified as Dumuzid.

History
Dumuzid is the name bestowed upon him by Astaroth when he ascended: in his human life, he was known as Thomas Mutton. When working at the Stray Sheep, he is simply known as Boss.

Born human, Thomas doesn't speak much of his mortal life. He mentions a long-standing problem with alcohol in his 20's and 30's where he would often end up in embarrassing and mysterious circumstances. He married after that, and subsequently cheated on his wife with a young woman while she was away on vacation. She reacted violently, and it can be assumed this is when he started having the Nightmares.

He climbed Ishtar's tower successfully, as Vincent does in the main game. Impressed with him, Ishtar granted him a wish: godhood, and a place as her consort.

Thomas still speaks fondly of his wife, despite their history.

It's not clear how old Thomas is, though Lindsay and Martha both speak of two men who succeeded in the Great Trials: one 300 years ago, who was given a fortune, and one 700 years ago, who was given the world. It could be assumed Thomas was given the world, godhood, and is 700+ years old.

Personality
Thomas spends the majority of the game dispensing romantic advice to Vincent by stealing other people's quotes. These quotes are usually damning to relationships, and meant to discourage him from trying to continue one with Katherine. This tendency to use other people's words continues during the final fight, where most of what he says is taken from other video games or pop culture.

Though a demigod, his cool facade is easily broken in the real world to reveal someone a lot more submissive, and easily intimidated.

He also has a reputation for being promiscuous; this is the main reason Ishtar gives for wanting to replace him.

Nightmares
Astaroth states that the Great Trials were created by Dumuzid, after he beat a version of them himself. He is the one that explains the trials' true purpose, and the one responsible for choosing each victim, using his occupation and business as a form of intelligence-gathering and keeping an eye on his targets.

He also constructed the Rapunzel arcade game, as a way to ease the shift into the nightmares by familiarizing his victims with its mechanics.

Although Vincent forced him to stop the nightmares when he became the Man of Legends, it's not clear if this is permanent, as Dumuzid ultimately answers to Ishtar's wishes.