Everybody needs that one friend they hate, right?
Eric the Cavalier may seem like a coward but Eric is a hero at heart, wielding the magical Griffon Shield.
Poor Eric; he was the butt monkey both in and out of the show. In-universe, it's implied he's the rich kid at school, whose father doesn't have any time for him, and that he just sort of invited himself along on the amusement park trip that ended up sending them all to The Realm because he doesn't have any real friends. He dislikes being trapped in this alternate reality, and since he isn't shy about letting that be known, all the other kids feel free to mock him for the way he feels. When he complains about the things they're going through, worse things happen to him. And that's because, out-of-universe, some parents' group insisted that the show needed a "message," and that the message should be "the group is always right... the complainer is always wrong." Yeesh. That's what passed for "pro-social" in the early '80s.
[he enjoys lording his wealth over all the poors he knows] Eric was given the role of Cavalier, which seems like a joke on Dungeon Master's part: like, yes, a cavalier is a name for a knight (originally any mounted horseman, from the same Anatolian-by-way-of-vulgate-Latin root that also led to words like caballero, chivalry, and cavalry), but in Elizabethan English, its meaning was expanded to also pejoratively encompass a knight's haughty attitude. So the stuck-up rich kid is cavalier? He sure is!
...
The cartoon writers hated what they were forced to do with Eric, but they found a way around it: yes, he still complained, and yes, he was still diagetically punished for it, but the writers' subversion of the mandate as the show went on was to usually make Eric right: like, he'd say that going into a magic swamp was a bad idea, the other kids would bully him into going along with them, and then it would turn out going into the magic swamp was a bad idea, and it got them into more trouble than avoiding it would have. But by not drawing attention to that part, the show kept the parents' groups from getting mad at them. Nice!