Their mothers are depicted in ' This Book Sucks' Their parents never appear in person the series or the comic books, though Beavis' mother is stated multiple times to be loose and to 'suck' in the comics. While they're not related, they have known each other from infancy and are always in the same house, growing up pretty much like brothers. Daria Morgendorffer has twice encountered him in this state, and is the only person to have successfully handled him. When Beavis becomes too hyper - sugar, caffiene, or drugs - he transforms into the beserker state of 'the Great Cornholio'. The duo can drive people (like Principal McVicker) to genuine breakdowns and cause mass destruction and chaos, but they're not intentionally cruel and malicious: they're genuinely too stupid to know any better.

One of their main interest is loud rock and metal music (they can sometimes be seen air-guitaring & chanting the riffs of favoured songs or headbanging to something), and they pour over and comment on any music videos they find - especially ones that 'suck'. Their extremely distinctive laughter has driven teachers to despair. They find many things 'cool', including insults and physical abuse directed at each other. The two are very, very, very dumb - in the Daria-less episode 'Trouble Urinating' they forgot how to pee - and are driven by hormones, junk food, and music that 'rocks'. Beavis is the more excitable and easily-manipulated of the two, while Butt-Head is the (slightly) more collected 'leader' of the duo.

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