Beavis has an underbite and a fixated stare on his face which rarely looks straight at the television viewer, but rather to the side. He is usually seen wearing a Metallica T-shirt, though in merchandising appearances, his shirt displays the slogan “Death Rock,” to avoid licensing issues. In Blood Drive he wears a Slayer shirt rather than his normal Metallica one.
Beavis works as a fry cook at Burger World and once defiantly revealed that he’s a fan of Bon Jovi to Butt-head, who dislikes the band and its leader Jon Bon Jovi. The episode The Final Judgment of Beavis reveals his birth date as October 28, 1979.
Beavis' name was inspired by a friend of Judge’s from his college days named Bobby Beavis. During the years of the series' run, Beavis' name was mispronounced by adults as, among other things, Beaver, Beatrice, Boris, Brevis, Joe, Paul and Travis.
Mike Judge once said in an interview that Beavis "is a zero" when it comes to intelligence; indeed, Beavis is often oblivious to what should be obvious. Generally submissive to Butt-head and willing to tolerate a large amount of physical and verbal abuse, Beavis nonetheless has limits. In Murder Site, Beavis was driven to attack and nearly kill Butt-head, who wouldn’t cease calling him “Butt-knocker", a term which Beavis resents. Beavis also stood up to Butt-head while they were watching a Rancid video: Butt-Head kept talking about it derisively, prompting Beavis to tell Butt-Head to shut up. When Butt-head reacted with fury, ordering Beavis never again to tell him to shut up and threatening to kick his ass, Beavis preemptively kicked Butt-Head in the testicles, told him to shut up again, and walked out of the room to get something to eat. In another episode, while the duo were watching a Bon Jovi video, Beavis claimed to like one part of the song, causing Butt-head to slap him in disgust. After being struck a few times, Beavis kicked Butt-head in the groin and proclaimed "Bon Jovi rules!" (This particular segment is featured in Prank Call, but only the version shown during the Super Bowl special).
In spite of his overt idiocy, Beavis possesses a number of character strengths. He can be inadvertently witty and, when discussing subjects that neither he nor Butt-head understand, he is more likely to guess the actual mechanisms at work. Also, on the rare occasion that a female exhibits interest in one of the duo, it is usually Beavis (as exemplified in the episodes: Vidiots, Another Friday Night, Teen Talk, Letters to Santa Butt-head in Christmas Special) who gets the attention; this could be because of Beavis’ somewhat childlike temperament, which is less off-putting than Butt-head’s crasser, more blatantly sexual approaches. For example, when the two encounter members of the opposite sex, Butt-head will typically lead off with a smug opening line such as, “Hey, baby”, which invariably flops; Beavis, on the other hand, will usually approach the woman with a less obvious “Hi!” or “Hey, how’s it going?” Easily influenced by Butt-head, however, Beavis will often imitate his buddy's cruder pickup lines. Beavis has also shown instances of insight on such topics as the true meaning of Christmas, or in his analysis of a video by Korn. However, in both instances Beavis seems to either be in a trance or possessed, and shortly afterwards displays no recollection of what he just said.
Beavis has a more volatile, unpredictable nature. His hasty actions usually end in disaster, ranging from getting deported to Mexico (Vaya Con Cornholio) to severely injuring himself (Woodshop). In early episodes such as: Home Improvement, Comedians and Stewart's House, Beavis displayed signs of being a pyromaniac. Though his obsession with fire remained an obvious trait, as the seasons progressed and network censorship pressures increased his fixation became more of a passing gag. In a deleted scene from the film, the character takes without asking the Declaration of Independence to use as toilet paper.
Beavis as The Great Cornholio.After consuming large amounts of sugar or caffeine, Beavis sometimes undergoes a radical personality change. He will raise his forearms in a 90-degree angle next to his chest, pull his shirt over his head, and then begin to yell or scream erratically, producing a stream of gibberish and strange noises, his eyes wide. This is an alter-ego named ‘Cornholio,’ a normally dormant persona. Cornholio tends to wander aimlessly while reciting “I am the Great Cornholio! I need TP for my bunghole!” in an odd faux-Spanish accent. Sometimes Beavis will momentarily talk normally before resuming the persona of Cornholio. Once his Cornholio episode is over, Beavis usually has no memory of what happened. In the guise of Cornholio, Beavis becomes a successful beat poet (Buttniks), and in Vaya Con Cornholio he is deported to Mexico after wrongfully being subjected to immigration detention by an agent of the INS. During his detention the agent and his superior attempt to make sense of the gibberish that is Cornholio, going so far as to look up the definition of "bunghole."
Beavis and Butt-head fighting.Though the closest of confidants, Beavis and Butt-head have a jaded, violent, and at times borderline sadistic relationship. Butt-head often insults and physically abuses Beavis (usually by slapping him). On occasion, Beavis will fight back or stand up for himself (Madame Blavatsky, They're Coming to Take Me Away, Huh Huh). His favorite means of retribution is kicking Butt-Head in the "nads". On at least one occasion Beavis has thrown the first punch. In Canoe he initiates a fight by smacking Butt-head across the head with a paddle (although Butt-head goaded him into doing it). Butt-head usually knows when Beavis is approaching his breaking point and will back off (as seen when he calls Beavis "Buttknocker" or insults Metallica one too many times).
Beavis is usually a follower, willingly taking Butt-head's instructions and cooperating in his endeavors. This appears to be a byproduct of Beavis' own general witlessness rather than any fear of Butt-head's abuse — as demonstrated in the alternate reality of It’s a Miserable Life, in which Butt-Head had never been born and Beavis was instead the dim but productive friend of Stewart Stevenson.
While Butt-head's main interest in life is "chicks", Beavis seems to be more interested in toilet humor and displays of violence. Beavis has a penchant for making off-beat sound effects to suit the occasion. Whenever he sees something that is arousing, he imitates a spring (“Boi-oi-oi-oi-oiiing!!!”) He sometimes blows a raspberry by puckering his lips. He occasionally does impersonations, such as of Principal McVicker (Speech Therapy), motivational speaker Mr. Manners/Mr. Candy (Manners Suck/Candy Sale), and Woody Woodpecker (Top O' the Mountain). During one episode, Beavis conspicuously reveals that he is sometimes prone to getting erections in the company of other men. A special ability of his is speaking backwards, as seen in Vidiots while the duo review a music video; however, he forgets how to do so by the end of the video. Beavis also displays a predilection for feces and things related to it, and in a high pitched tone will often enthusiastically utter the word, “poop,” or will say the word "plop" to indicate a bowel movement. He frequently pulls down his pants during music video reviews. He also took Kaopectate once after hearing it is for diarrhea under the misconception he would get diarrhea; he was only soothed by an enormous bowel movement which he saved in his dresser drawer, much to Butt-head's disgust. Beavis sometimes displays examples of the idiot savant when slapped hard by Butt-Head or when attempting to pass out by holding his breath and blowing into his thumb, in which cases Beavis starts to make intellectual statements usually regarding the music videos he is viewing.
Beavis's family is occasionally referred to but never seen. An example is when Beavis states: "My mom's a slut... meh heh heh." According to discussion during some music video segments, Beavis’s mother shares her son's peculiar hairstyle, is somewhat plus-sized, and (most significantly) is a slut. While Beavis is conscious of his mother's promiscuity, it doesn’t seem to bother him much, as he often laughs along in agreement whenever Butt-head brings it up (in fact, when Butt-head refers to Beavis's mom as a whore, Beavis nonchalantly says "She's not a whore, she's a slut, she doesn't charge for it".) The irony, however, is lost on Butt-head, whose own mother's promiscuity is implied in Beavis and Butt-head Do America.
In Beavis and Butt-Head Do America Beavis is reunited with his biological father, who seems to exhibit the same pyromania obsession as Beavis, as well as an overt physical resemblance. He is said to be a drifter and a one-time roadie for rock band Mötley Crüe. However, they remain oblivious of their father-son relationship and part ways before they make the connection.
In the 1996 Paramount comedy, Beavis and Butt-head Do America, at the beginning during the King Kong/Godzilla-like scene, Beavis is called Beaviszilla, however, when he sees Butt-head, he calls him by his real name.