Stewart Stevenson (voiced by Adam Welsh in the original run of Beavis and Butt-head and by Mike Judge in the 2011 revival) was a classmate of Daria Morgendorffer at Highland High. He was a complete wuss, as eternally symbolised by wearing a Winger shirt.
He usually thought Beavis and Butt-head were his friends - they were not - and trying to impress them. On some occasions, he was aware of the damage they cause and tried (futilely) to mitigate it. As well as the arseholes bullying him, exploiting him, and dissing him for sucking, in "Drones" Beavis actually forgot Stewart was alive and they'd seen him yesterday.
Stewart's family are church-goers, with their church run by a pastor ("The Great Bungholio"). He's also member of the Positive Acting Teens (PATsies), and hangs on the words of televangelist Clark Cobb & his horribly lame sock puppet ("Walkathon"). In "Walkathon", he genuinely thought Socko the sock puppet was "cool" - it was not.
We know from "It's a Miserable Life" that Butt-head is personally responsible for destroying Stewart's self esteem. If Butt-head hadn't existed, Stewart would be a more assertive, active figure - as shown by him wearing a Poison shirt instead.
Daria very rarely encountered him in the show - they were shown to be classmates in "Water Safety" but there's no direct interaction between them in that episode - but repeatedly in the comics. "Tales from the Dim" shows her opinion of him: very low, lumping him with Beavis and Butt-head as people it was "terrifying" to see at her house. She did go to his birthday party in a later issue but didn't look like she wanted to be there at all. (Of course that's her default face) In "Witless", she threatens him - quite seriously - with violence, to ensure Beavis and Butt-head would be abandoned in Amish country.
Their final encounter was in a letter page, where she told him "shut up, Stewart" while he was in mid-sentence.
For legal reasons his Winger shirt became an "I [heart] UNICORNS" T-shirt in spinoff media.
He will sometimes get mentioned or have a walk-in in Daria fanfiction, if that fanfic is set in Highland.