The Greaser Dogs are a gang consisting of three dogs named Cliff, Shriek and Lube. They serve as the main antagonists of the series. They act no differently than school playground bullies, picking on anyone either weaker or different than them, usually by attacking them in a way that they refer to as pounding. They pick on CatDog (mostly Cat) because of their freakish nature and their hated for cats as revealed in the first episode, "Dog Gone". Because Dog has Cat for a butt. Dog sometimes gets along with them because he's a wolf-like form as well. They initiated him in the gang after he had proven his worth. The Greaser Dogs also having the fear of a tick, which usually renders them helpless in almost any situation.
Cliff: (voiced by Tom Kenny) The leader of the Greasers who is a deformed dog. He wears a black jacket with a picture of a cat on the back of it. He is very short tempered and speaks with a gruff Brooklyn accent. Eddie was accidentally glued to his jacket which them turned into "Squirrel Dog". Once this happened, Shriek and Lube kicked him out of the Greasers because he was a two-faced freak. However, once he was free from Eddie, he returned to his old bullying ways and re-joined the Greasers. In another episode, he volemnly vowed to never bully anyone again but it didn't last long. In the episode, soft sides of Cliff have been revealed, such as love for ballet and cashmere. The episode "Beware of Cliff", he proved that he's not.
Shriek: (voiced by Maria Bamford) The only girl in the Greasers. She is a tiny poodle with a squeaky, raspy voice. Though she's as tough and loyal as the other two, she's very emotional romantically and has a crush on Dog (though he never appears to notice) and frequently hides it from the other Greasers. Shriek will not hit Dog, she'll only hit Cat. In the episode "Rich Shriek Poor Shriek", she came from a rich family, but she didn't like the posh life, so she left home and become a greaser. She pointed out to Cliff and Lube that she's actually a girl in which both Greasers finally realized it and screamed.
Lube: (voiced by Carlos Alazraqui) A Hound dog, and the slowest and sweetest one of the group. He'll forget what he's saying and slur his speech. Despite this, however, he can speak perfect Spanish. He's the most loyal of the three Greasers. Despite his dull wit, like his parents, Lube has lots of musical talent and can sing very well. It is important to note a character design modification that occurred after the first episode; in the premiere episode "Dog Gone", Lube appeared with black dot eyes and long brown hair that extended down to his nose. In subsequent episodes, his appearance was changed and remained that way until the end of the series. In one episode he rolls up his right trouser and takes off a wooden leg. He also works part-time as a mechanic. His parents, a cat mother and a dog father, appeared in the series finale and said that Lube got separated from them a long time ago. Also in the series finale, Lube is shown to have had a sister, who tries to marry Cat.
- The Greasers pose similarities to several troublesome trios. They are like the Kanker Sisters as all three trios usally get away with their crimes.
- They are similar to Shenzi, Banzai and Ed of The Lion King as both canine trios have two boys and a girl. Also, both Lube and Ed are stupid and Ed is voiced by Cat's voice actor, Jim Cummings.