Although personally hygienic, polite, caring and practical, Rocko has an almost pathological tendency to neglect his living space and he has anger management issues. Rocko enjoys collecting comic books and likes rainbows. Jean Prescott of The Sun Herald described Rocko as a "pudgy little wallaby" who tries to "do what's right" and is devoted to his friends Heffer and Filburt as well as his dog Spunky.
Common Sense Media reviewer Andrea Graham, whose review is posted on Go.com, describes Rocko as "paranoid and obsessed with cleanliness" and that he initially perceives his neighbors to be "loud and messy." Graham describes Rocko as accepting of his neighbors' faults and seeing the positive qualities within them; unfortunately, that has also led him to becoming a bit of a doormat in the eyes of others (no matter how many times a person wrongs him, he always forgives them, despite knowing they will wrong him again in the future). In an early character profile presented to the networks Murray described Rocko as "a young anthropomorphic Woody Allen, who has just moved away from his home into a surrealistic world."
Rocko wears a blue shirt with purple triangles and orange shoes. His eyes are white with black pupils and he has a black nose. He also has beige skin and fur. His fur and skin were yellow in Trash-O-Madness. He is also noticeably shorter than the other characters.
Rocko first appeared in a never-released comic, where he has the name "Travis". Joe Murray, creator of Rocko's Modern Life, believed that the personality of a wallaby suited Rocko after observing a zoo wallaby. Murray wanted to get his comic into syndication. Afterwards Murray made substantial changes to Rocko. Murray added that the personality of a wallaby mirrored Rocko's humbleness and his tendency to keep his frustrations to himself instead of publicly complaining about them. In the original pilot for Rocko's Modern Life, the animators colored Rocko yellow. One month before the first episode was submitted to the animation studio in the free Korea, Murray changed the color when an toy company refused to license the character after citing that Rocko looked too similar to a yellow character used in one of the company's existing products. Murray fought the changes with the Nickelodeon executives; in the end the executives insisted on changing the color, so Murray changed the color to beige and disliked the choice. On his website Murray said, "He was always yellow to me." Murray said that the company later backed out of the commitment and did not create the plush series.
Murray auditioned Alazraqui in San Francisco, and chose him as the voice actor for Rocko. Jeff "Swampy" Marsh, a storyboard writer, describes Alazraqui's voice for Rocko as "not really an accurate Australian accent"; according to Marsh the team used the voice as Alazraqui used the voice for the pilot.
Murray said that as the series progressed he adjusted Rocko's design from episode to episode to be more "animator friendly." According to Murray, when he created independent films and the Rocko's Modern Life pilot, he created all of the character layouts in his mind and other animators used the layouts to create works. Murray said that when Rocko became "high volume," Murray taught Americans and Koreans how to draw the characters. Murray described Rocko as the most difficult character to draw, and he said that therefore he decided to adjust his character design in order to assist the overseas animators. Murray said that as he and the directors continued to "quickdraw" the character changes to the design "naturally" lessened the "victim, paranoid" aspect and gave the character a "happy personality."
According to George Maestri, Rocko has no family name because the writers did not think of a family name that they desired. The writers considered the family name "Stretchbrain" because the character's brain popped out of his head during "odd moments." The writers scrapped the idea, leaving the character with one given name. Some websites, including Hot Topic, give him the family name "Wallabee" and the middle name "James". In "Dental Hyjinks," the first story of the Marvel Comics Rocko's Modern Life series Issue #1, the nurse addresses Rocko as "Mr. Rocko."
According to Not Just Cartoons: Nicktoons!, Rocko's age is 20.
In the television show, in his day-to-day life, Rocko worked as a cashier at (and briefly as the boss of) a local comic book shop called Kind of a Lot O' Comics which is owned by Mr. Smitty and sold mostly Really Really Big Man comics prior to his current unemployment which is because of that store replaced by an instant-print kiosk. Rocko originally worked at Super Lot-O Comics, owned by chairman of Conglom-O, Mr. Dupette, Ed Bighead's boss. In the television show, his other jobs include tattoo artist, plumber's assistant, and speciality phone operator (possibly a phone sex operator), a product tester at Conglom-O, a tow truck man, an underwear model, and a cartoonist for the program Wacky Delly.
Rocko's neighbors are Ed, with whom he has a semi-rivalry, and Bev Bighead. Bev considers Rocko a very sweet neighbor. He and his dog Spunky, who often eats the neighbors' salmon bushes, are a source of constant annoyance to Ed.
Rocko's best friends are Heffer Wolfe, a steer who eats a lot and was adopted and raised by a family of wolves, and Filburt, a bespectacled and nerdy turtle with neurotic Woody Allen-esque mannerisms, who often feels nauseated. He is also good friends with his dog Spunky. Although he gets along with Heffer, he does not enjoy Heffer's company in Bedfellows. He is also good friends with Dr Hutchison, a cat who wears a huge grin and is a doctor who usually helps Rocko with his problems. Although she is a great help for Rocko, she does tend to get violent with him in episodes such as Closet Clown and Turkey Time, as well as Heffer, Filburt, and the Bigheads.
In early concept sketches Murray indicated that Rocko bears a strong crush on a character named "Melba Toast". Rocko expresses this trait in Season One, bearing a crush on the unseen character until he discovers that Melba has a serious boyfriend. Melba is only later mentioned by Heffer (Season 4 in "Pranksters") as an April Fool's joke, pretending to spot her in a foodcourt and waving her over, making Rocko nervous as he states that he can't look at her because he is still in love with her.
In subsequent episodes Rocko bears crushes for other characters. In S.W.A.K., Rocko has been vying for the attention from the pretty kangaroo mail-lady named Alicia, that comes to his door every day; he writes her a love note that he is too scared to send so Heffer does it for him instead. Rocko fails to retrieve the letter and gets the impression that the mail-lady would rather go out with Heffer. This turns out to be a joke on the mail-lady's part and she actually returns Rocko's feelings. In I See London, I See France, Rocko falls in love with a girl named Claudette, who turned out to be his wallaby pen pal from Paris, but she is more interested in Heffer. In Wallaby on Wheels, Rocko falls for a roller-skater girl named named Sheila and tries to impress her by learning to rollerskate from Heffer. He becomes jealous when it is implied that she is in love with Heffer and tries to impress her by doing a dangerous stunt. In the end she becomes attracted to Rocko after he saves Heffer and Rocko teaches Sheila how to use a jackhammer.
"Hehe Oh My"
"Oh Baby, Oh Baby, Oh Baby"
"Garbage day is a very dangerous day"
"Heh heh. Good as new."
"I'm a wallaby on wheels."
"I don't want to sleep! I don't need sleep! I am the walking living!"
"Excuse me, Earl... but garbage and dogs are not part of a balanced diet."
Rocko's shoes might be a reference to Playskool's toy "Mr. Potato Head".