Robot Default is a Mechanical and the main protagonist of Robot and Monster.
Since birth, Robot has been locked in a rivalry with his older brother, Gart Default. Often, Gart would play a game of Rock, Paper, Scissors with Robot, and always win due to Robot only being able to use scissors (while Gart, on the other hand, has the "cool, four-fingered hands"). According to "Between Brothers," Robot's inventions either annoyed or terrified the Default family, and have possibly made him the laughing stock of the Defaults. Since he was a little kid, Robot has been close friends with an Organic named Monster Krumholtz, though, according to Monster himself, he had been told not to trust Robot and his inventions. Throughout their friendship, Robot has seemed to use Monster as a test subject for his inventions and has even pranked Monster in school. Despite this, Monster has stuck with Robot and cheered him on, remaining a close friend and eventual roommate. He values his friendship with Monster so much that he even sacrifices himself to save Monster's life, as stated in "Spare Robot."
Robot has, as stated in the episode, "Ogo's Friend," been a rival to another Mechanical named Lucy. The rivalry started since first grade up to the twelfth grade, and even through college (and apparently it continued into a weekly vocal jazz ensemble). However, Lucy always managed to beat Robot with her own inventions, despite not remembering who he is actually.
Apparently, after completing college, Robot somehow ended up working for Default Industries in the Blinking Light Factory in quality control, where his older brother is the boss. Luckily for him, Monster works alongside him, making the seemingly boring job endurable. The two live in a three-story apartment building, taking up the top floor. The only other known tenant is their annoyingly clingy neighbor, Ogo, who seems to have a very creepy obsession with both Robot and Monster. However, it's possible that their landlord, Mr. Wheelie, lives in the building as well, taking the first floor.
Robot and Monster own a blimp which they have used in a few episodes. Robot attempted to enter the blimp in a race, but, in order to compete with Gart (who had also entered with an expensive and fast blimp of his own), Robot decided to work on the engine to improve its performance. However, Monster's younger sister, Globitha Krumholtz, was invited to stay during the weekend Robot was working on the blimp. In the episode, "Adventures in Babysitting," it is revealed that Globitha is clingy towards Robot, and has injured him in the past when she has tried to help him. Her clinginess even gained the attention of Ogo in the same episode. Despite disliking her obsessive behavior and eventually scolding her for it, Robot does care about her feelings and rescued her (with Ogo's help) when the blimp got out of control with an upset Globitha in it. The runaway blimp won the blimp race and Robot made up with Globitha.
In various episodes, it has been hinted about Robot having had a miserable childhood, as he sometimes mentions his father, who might have laid a negative impact on his earlier life, resorting to Robot developing an open dislike for him. In "Hornica," he even referred to Monster's father, Lev Krumholtz, as the "best dad in the world," and calling his father "not even close."
Most of the Default family dislike him, even going as far as to try and keep a family party secretive from him, as seen in "The Party." His mother displays massive affection for his brother, Gart, while she often scolds Robot for simply being himself; she doesn't refrain from calling Robot a disappointment, and this, although hurts him deeply every time, is often ignored by Robot, who seems immune to her harsh comments.
Nick.com's official description of Robot is the following:
"As a Quality Control Inspector at the Blinking Light Factory, Robot is doing exactly what he was designed to do. Like any other Mechanical, Robot should be happy with fulfilling his purpose, but the amateur inventor and self-proclaimed genius knows that he is destined for something bigger. The only problem is, his ideas and inventions get him nowhere. He feels like the world is trying to keep him down. So frustrating! And it doesn't help that his supervisor at work is his know-it-all older brother, Gart. Lucky for Robot, he isn't alone! Monster believes in him all the way. That's what best friends are for!"
Robot is depicted as being small; his body is squat and rounded. His body is an orange color, with his arms being a more rusty color and shinier than his body. He has two dark gray fingers that he sometimes uses as a wrench on each hand, and four wheels for feet. His legs (if they can be called that) are thin and extendable, allowing him to increase his height to grab things out of reach. His eyes are thick, usually semicircular, discs that protrude from his head via short eyestalks. They can change shape slightly to express emotions; they sometimes become circular when he's amazed or beaming from joy. They also have eyelids which help express emotion as well. Robot's eyes are yellow in color, with orange trim, and black pupils. It is shown that Robot's eyes are apparently made of glass, as they have shattered in "Pinball Wizard." Robot's rotound body houses a hatch with two hinges on the right side (from his point of view). The hatch lid has a large, yellow, capital "R" (or a lowercase "r" when he was younger) on it. Inside seems to be a near hollow cavity that houses his "heart" (a gray box with a pink heart on it that seems to be attached to the rest of the insides through metallic "arteries") and acts as a small storage compartment. Robot is known to be able to reach inside and grab internal parts (such as his gyroscope) and pull them out. Robot's head is attached to his body with no neck, much like Gart (and probably the rest of the immediate family). Atop Robot's head is a short, wavy antenna that constantly sways when he moves. In several episodes, it is shown to be removable, like much of his limbs and body parts.
It should be noted that he apparently has a skeleton, as seen in a flashback in the episode, "Adventures in Babysitting."
- He has the most fears out of anyone else in the show: he has a fear of getting hurt when playing Pole-O as revealed in "Game Boys"; he suffers from pupaphobia (fear of puppets), as revealed in "Speak Marf Speak."
- His antenna can determine his grease intake as discovered in "The Blimp"
- It is revealed in the episode, "Doctor? No!," that he has a fear of lollipops.
- When furious, he explodes as shown in "The Prince of Scamtown."
- His heart has stopped three times so far. In one incident, Monster smacked it a few times to get it started again, in the second Robot pulled a knob much like a lawn mower. The third incident had Robot using wires to jump-start himself.
- He has feelings for J.D., however, in "Biker Girls," there was a slight hint of attraction between him and Spitfire.
- In "Hornica", it is revealed that Robot may have a disheartening dislike for his father, as in the beginning of the episode he is shown to have great admiration for Monster's father, even calling him the "best dad in the world".
- He has the same voice as Dan from Dan Vs., incredibly speculated by many viewers when the show first aired. They almost share the same personality as they are both short-tempered.
- He has trouble making friends beyond Monster, Ogo, J.D., Spitfire, Nessie, and perhaps Perry and Punch Morley, especially evident in "First Impressions."
- It was revealed in "Apartment 3 1/2" that he used to have a Captain Spangleshorts action figure when he was a kid which his father made him throw away.
- His ambition for inventing is very similar to Rodney Copperbottom from the movie Robots.
- Robot being disrespected and shunned by his family is very similar with Sid the Sloth from Ice Age: Continental Drift; the only difference is that Sid's family fully abandoned him, along with his grandmother, while Robot still keeps some contact with his family, and his own grandmother disrespects him as well.
- Robot shares a simlar life to Sirius Black from the Harry Potter series, both characters are the black sheep of their family (Robot not being snobby and his inventions and Sirius not being hateful towards to none pure wizards and witches) and both had been welcomed by their best friends' family.
- Robot often mentions his father, but he has never appeared in any episode except for a cameo in one of the Blinking Light Factory's portraits in "The Party."
The gallery for Robot can be found here.