Black Doom is presented as a highly ruthless, sadistic, and power-hungry tyrant. He regards humans as pathetic creatures that have led to the destruction of their own planet. Black Doom has neither affection nor sympathy for anybody or anything, including his own army and his creation, Shadow. He gladly took the lives of his own army in order to destroy Central City, the city he choose for the site of the comet when it was teleported down via Chaos Control. Black Doom has a dark lord persona in which he committed horrible atrocities throughout the story, such as attacking six cities and killing millions, blowing up Central City, and torturing the humans and having his army consume their bodies. He also does not forgive any mistakes or failure, no matter how difficult the task on Shadow's part may be.

Black Doom's plans for the planet Earth extend much further than simply controlling the planet. His main goal is to take control of the planet and then have him and his armies feed off the humans, which he states are a great energy source for them. According to Doom, once the planet is under his control, the humans will never see the sun again and the planet will cease to be blue. It seems Doom wants to conquer the planet as a step closer to conquering the entire universe. He has no respect for humans, as he sees them as fools who have committed crimes against themselves, and believes that he is doing them a favor by using them as a food supply for his race.

While Doom claims that he has Shadow's best interest, he does not care for him at all and is only interested in his power. He often tried to manipulate Shadow in order to turn him against humanity, but this caused Shadow to see Black Doom as his ultimate enemy in the end. Doom sees Shadow as his gateway to the Chaos Emeralds and his unusual skills would make him a great addition to the army. Doom often used Shadow to do tasks that would give him an advantage, such as destroying the human's data servers so information could no longer be transferred among the humans, awaking the temples to be used as weapons, and even attempting to assassinate the president.

Unlike other Sonic villains, Black Doom is completely devoid of any sense of humor. He is quite arrogant, claiming that he not only rules the universe, but that he is the strongest being in the universe as well (to the point of saying he is immortal). Despite all this power, he is still defeated by Super Shadow, which ironically was his fault, as he left the Chaos Emeralds with Shadow when he warped away to transform to Devil Doom, believing their power was useless against him. He reconsiders this belief during the final battle, admitting he'd underestimated the Emeralds' powers.

Black Doom was voiced by Sean Schemmel, but I'll allow some leeway on this audition: 

https://www.youtube.com/watch?v=E2r7IXnasD8