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 from an acquaintance of Judge’s during his college days named Bobby Beavis. During the years of the series' run, Beavis's name was mispronounced by adults as, among other things, Beaver, Beatrice, Paul Lenig, Brevis, Joe, Paul and Travis.
Dan Tobin of The Boston Phoenix described Beavis as "the sidekick and follower" who developed into "more of a loose cannon."
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 inexplicably 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 reacts with fury, ordering Beavis never again to tell him to shut up and threatening to kick his ass, Beavis preemptively kicks Butt-Head in the testicles, told him to shut up again, and walks out of the room to get something to eat. In another episode, while the duo were watching a Bon Jovi video, Beavis claims to like one part of the song that is cool, causing Butthead to slap him. After being struck a few times, Beavis kicks Butt-Head in the groin and proclaims "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.
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, and then begins to yell or scream erratically, producing a stream of gibberish and strange noises. His eyes grow wide. He becomes an alter-ego named ‘Cornholio,’ a normally dormant persona. Beavis pulls his shirt over his head and wanders aimlessly, 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 being picked up at Burger World by an INS agent. 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 is usually a follower, willingly following most of Butt-head's instructions and cooperating in almost all of 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 future of It’s a Miserable Life, in which Butt-Head had never been born and Beavis was instead the friend of Stewart Stevenson.
“My mom’s a slut . . meh heh heh.Beavis’ family is occasionally referred to but never seen. According to some music video segments it is said that his mother shares Beavis’ peculiar hairstyle, that she is somewhat plus-sized, and (most significantly) is regarded as a slut. While Beavis is conscious of this, it doesn’t seem to bother him much, as he often laughs along in agreement whenever Butt-head brings it up.
In Beavis and Butt-Head Do America Beavis is reunited with his biological father, who seems to exhibit the same pyromania obsession. He also shares an overt physical likeness. He is said to be a drifter and a one-time roadie for rock band Mötley Crüe. However, they remain oblivious to their father-son relationship and they part ways before they make the connection.