Rat is one of the main protagonists in the comic Pearls Before Swine. He's a bitter and cynical figure who often expresses negative and antagonistic things towards the various aspects of life in their world. A good portion of the comic's humor is derived from his approach to daily life and sardonic comments.
In the Series
Rat is a megalomaniacal rat who lives with Pig. He is usually self-employed and is mostly a writer. He hates virtually everyone, even destroying Pig's computer when his friend Goat was looking for him and not reassuring his friend Pig when he asked if he was fat. He thinks he knows everything, but he is just as idiotic or seeing only the bad side on a constant basis. He is rather xenophobic and thinks the politics has something to do with too many people.
His religion is ambiguous, he is friends with Satan and made up his own denominations like Cheesepuffology, and he once wrote a story about a misanthropic donkey named Danny Donkey who once recommended that the people should destroy the Earth rather than save it in an attempt to save the Earth, and a pair of buttocks and his family. He hates his life as evidenced in a July 4, 2010 strip and is extremely idiotic towards women. He also once attempted to round up a club of fellow misanthropes but predictably failed in that endeavor.
Despite his attitude, he has been shown to care for Farina (a germaphobic pig in a plastic bubble), and was heartbroken when she left. In a recent strip, he also went out into the park to look for Pig, presumably hinting that he cared about him.
Acts
Nevertheless, Rat has been a villain protagonist on numerous occasions. In a baseball game against the Crocs, Rat bet Zebra's life on the line, showing absolute apathy to Zebra's concerns (flatly telling Rat that it should be "encouragement" for Zebra to win). His relationship with Pig often consists of verbally and physically abusing his friend for Pig's well-meaning but stupid behavior. In general, he shows great contempt for stupid people, although this also extends towards people he considers to be stupid, which includes optimistic folk.
Rat also often criticizes Stephen Pastis for his crude comic strips. This criticism ranges from verbal insults to threats of physical harm to outright acts of harm, such as beating Pastis over the head with a baseball bat or dropping an anvil on him. This association is generally antagonistic with Rat once taking over the strip and having a "Ratepillar" devour everyone in the comic.
In addition to this, Rat has committed some murders. For example, he once bit the head off a gingerbread man (who, like many things in the Pearls universe, is a sapient object). While hosting a radio show, he told a man who claimed to have his brain taken by aliens to drive off a cliff. And his arguably most vile act was killing a man so he couldn't reproduce. So overall, Rat is a dirty rat.