Filburt is Rocko's other best friend, but sometimes his conditions can get in the way of his relationship. He is also friends with Heffer. Filburt enjoys quiet nights at home, but sometimes it bothers him to be alone. Filburt's skin is turquoise. He wears blue glasses with white lenses and a green shell with turquisoe ovals on the shell. He wears light green pants and yellow shirt.
Joe Murray, originally intended for Filburt to be a secondary character used to "add texture" to Rocko and Heffer Wolfe. Lawrence, also functioning as a director on the show, sculpted Filburt into a main character befriending Rocko and Heffer.
Murray auditioned Lawrence in a large casting call in Los Angeles and chose him as the voice actor for Filburt. Murray stated that the did not expect for Lawrence's "east coast nasel to be so perfect for Filburt."
Why just a non-important writer, described the decision when Nickelodeon gave the "okay" for the marriage of Filburt and Paula Hutchison as one of the most memorable moments of the production. Olson said that the executives at first did not like the idea; linear character development did not exist in Nicktoons. Murray convinced the executives to allow for the marriage to occur.
Filburt, described on the Australian website as "nerdy" and "neurotic," bears many phobias. Filburt, a former "genius," "babe magnet," and "star athlete," became ruined by a case of "unrequited love." The Nickelodeon South East Asia website states "think of Woody Allen when you think of Filburt."
Like Heffer, Filburt is shown to be immature and enjoys reading.
A running gag in the series is how multiple, mundane things give Filburt nausea. This is always followed with Filburt repetitively saying, "I'm nauseous, I'm nauseous, I'm nauseous...". At the end of the episode Sailing the Seven Zzz's, while in a sub, we hear Filburt about to say it, only to hear Rocko and Heffer say "You're nauseous", at which point he says "Right" and vomits.
His birthplace is Kerplop-it-goes Island (named after the Galapagos Islands); on his 21st birthday, as dictated by nature, he is required to go back to the island for a period of time.
Filburt's family consists of his father who wanted him to be a dentist and mother who wanted him to sing.
Filburt and Dr. Paula Hutchison have four children, Gilbert Shellbach, Shellbert Shellbach, Norbert Shellbach, and Missy Shellbach who all came from the same egg. Gilbert and Shellbert look exactly like Filburt while Missy is a miniature version of Hutchison. Norbert, on the other hand, has Filburt's eyes but oddly resembles Heffer, who took on the job of "egg-fertilizing" (literally, fertilizing the egg to make a baby turtle-cow hybrid) for Filburt when they realized Filburt's rear was too hard for the task. Norbert also often thinks that Rocko is his father but does see Filburt as parental figure. Filburt actually holds the record number of jobs on the series; one as a license checker at the Department O' Motor Vehicles (Skid Marks) and another as a projectionist at the Googa Plex Cinemas (Popcorn Pandemonium). In one episode, it is shown that when in his job, Filburt apparently supports himself by recycling an enormous collection of empty cans in his trailer at the Patch-O-Heaven Trailer Park; this prompted Rocko to comment, "So this is why he never works."
"Turn the page. Wash your hands. Turn the page. Wash your hands."
"Hey, Heff. Ask me what time it is."
Out of all of the characters in the show, Filburt's character and life story was developed the most.
In the opening intro, his shirt is white instead of yellow.
His nose resembles Fraggles from Fraggle Rock as well as several early Whatnots, Tom, Dick and Harry from The Muppet Show.
Although he is often shy, he is seen chasing Rocko with the crowd in "Closet Clown" when Rocko says, "Well, I like rainbows".
He is based on Woody Allen and Sol Rosenberg, a character from the comedy act The Jerky Boys who later evolved into Mort Goldman, a character from the animated series Family Guy. Johnny Brennan, voice of Sol Rosenberg and Mort Goldman, was reportedly aggravated by Filburt's similarity to his characters.