Phil, the Prince of Insufficient Light is the ruler of Heck and the Pointy-Haired Boss's brother. As the ruler of heck, he "darns" people who commit minor infractions, such as taking two ketchup packets when you only need one, or borrowing copier paper for the laser printer. His darnings include equally minor punishments, such as sitting in the secretary's cubicle or being stuck with an annoying coworker for hours.
He also maintains little contact with the PHB. In the strip where it was revealed they were brothers, it was also implied that the two had not seen each other in a long time, and that Phil was unaware his brother worked for Path-E-Tech Management.
It is not exactly clear what species Phil is. Since he is the brother of the PHB, it can be assumed he was born human, but he also has horns and a tail.
At one point, he merged Heck with a non-alcoholic beer company, and in the subsequent synergy, was fired. He came to work for the Analogy Police, where he met Asok. The intern attempted to get the PHB in trouble for comparing him to a mink on a mink coat, but phil refused to get involved, and instead told him not
Evolution of Phil
Less than a year into the run of Dilbert, Scott Adams wanted to introduce the devil as a recurring character in the strip, but his editor talked him out of it. Scott Adams argued his case, but ultimately compromised and created Phil, which turned out to be a better move. Phil fit into the strip's world better than the real devil would, and, to date, Scott Adams has not been accused of being in league with Phil.
Some people noted the facial similarities between the Pointy-Haired Boss and Phil and asked if they were related. Scott Adams liked the idea, and eventually made a short story arc that revealed that they were, in fact, brothers.