The title character is a misanthropic, three-foot tall, bipedal, gray aardvark. Cerebus is intricately tied to the religious and political fate of the fictional world of Estarcion and becomes, at various points in the storyline, a mercenary, a Prime Minister, a Pope, a house guest, a bartender and a messiah. Cerebus refers to himself by name, in the third person, with occasional exceptions in the early issues. The name was originally an accidental misspelling of Cerberus.

Cerebus is a morally ambiguous character, at times sympathetic and at others unpalatably callous. He is often foul-mouthed and uncouth, has a vicious temper and loves getting drunk, to the point where he could be considered an alcoholic. In the "Guys" story arc, Cerebus is described as having "a self-absorption that borders on the pathological." In the story arc known as "Church and State", there are two notorious scenes where Cerebus, after becoming Pope, uses brutal methods to teach twisted morality lessons. After a mother begs Cerebus to bless her baby, he does so and then hurls it away, and later kicks an old man off the roof of a hotel. Despite his moral deficiencies, he is brave, crafty, and can show genuine affection to those he considers his equal or those he has feelings for. He is also a skilled tactician and strategist, is very proficient at hand-to-hand combat, and has a knack for improvisation and for being able to talk his way out of sticky situations. He also has some skill with magic, although his talents lie mainly in recognizing magic and dealing with it rather than utilizing it. Sim has described Cerebus' voice as sounding like George C. Scott's.

It is revealed in the "Reads" story arc that Cerebus is a hermaphrodite, possessing both genders' genitalia and reproductive systems.

Cerebus' most unusual quality is an innate "magnifier" ability that he possesses for most of the series' run. This ability, which he shows little to no conscious awareness of, is a quasi-magical tendency for events to fall into place around him and become unusually focused and ordered, sometimes with effects that appear to be paranormal, then fall back out of place into chaos in his absence. This ability also affects the people around him to varying degrees.

It is also of significant note that Cerebus is the longest running U.S. comic series with the same writer. Dave Sim (Writer/Artist) started Cerebus the Aardvark in December of 1977. The series went for 300 issues, 6000 pages, all the way through March 2004, making it, as Sim calls it, "the longest narrative in U.S. history."