Eric is one of the best-documented characters of the gang, if only because he insists on talking about himself. Every chance he gets, he turns the topic back on his experience, his opinions, his insights. The gang must have been highly tolerant toward Eric; that kind of trait could have caused lesser souls to hog-tie the loudmouth and hand-deliver him to the nearest Orc.
What Eric talks about most is his family's money--some of which he manages to produce out of a pocket in his armor(?) in "In Search of the DungeonMaster"; but the greenbacks vanish as soon as they appear. Money stayed a high priority in "The Garden of Zinn" when he accepted the offer to marry the Queen only after seeing a chest of gold and jewels. His description of Demodragon is that it's "bigger than my dad's bank account". When he was through playing in the backyard as a kid, he didn't simply go inside: the gardener picked him up in a golf-cart. He dismisses the flower that causes all the trouble in "Beauty and the Bogbeast" by saying his mother's garden had better blooms than that.
That's the only time we hear about Eric's mother, by the way. As for his father, Eric's comparison of his dad to Rahmoud in "City at the Edge of Midnight" is fascinating: "[Rahmoud's] better than my dad ever was." The cliche of the uptight, emotionally distant upper-class white American family was well-worn even in the Eighties, but it may well be part of the dynamics that shape Eric's personality.
Is it safe to say that Eric learned his biting wit and sarcastic manner by being the target of his father's verbal barbs? I believe that a fair amount of ridicule around the house gave rise to the dread uncovered in "Quest of the Skeleton Warrior" when Eric says "I wouldn't leave the house if I thought people were going to laugh at me." Ironically, since he talks about himself so much, it is the sign of an extremely fragile ego, to constantly defend oneself for fear of being torn down.
Defense is the keyword in the weapon Eric is given by DungeonMaster: a shield that can withstand literally anything: dragon's fire, tons of rock, magic spells cast by Venger. This weapon of the Realm is highly symbolic of Eric's life in the "real" world: shielded by wealth and privilege. In the Realm, he has to learn to extend his shielding influence to others.
School may have been another source of disparaging sarcasm. He doesn't seem to be a stellar scholar. He complains in "The Time Lost" that he flunked history twice and got by with a C- the third time. In "The Last Illusion", when DungeonMaster says that "when things are worst, things will be their best", Eric's comeback is "Try telling that to my old algebra teacher."
Eric has a grudging admiration of Hank, perhaps seeing Hank as a version of what he wants to be. He pokes around the edges of Hank's authority over the group, not willfully or defiantly but semi-seriously, like the adolescent he is. When the time comes for him to actually assume command, with Hank spirited away in "Winds of Darkness", he more than rises to the task. But he doesn't do so as an egomaniac. He takes command for one reason: to get Hank back to that he can resume command.
Eric provides a lot of comic relief in the series, and the more I think about it, the more I think it was a good move to have him voiced by Don Most. Don is best remembered as Ralph Malph of the Happy Days tv series. That gave him a lot of training in comic timing, and it shows in Eric's patter.
Earlier I mentioned Eric and the Queen of Zinn, who appears decked out in the kind of brass swimsuit style that characterized bad fantasy and science-fiction of the 1940s. There's no hint in the script that Eric--a teenager, remember--entertained any carnal thoughts about the Queen of Zinn. That may seem unrealistic, but there's only so much you can show on American TV. He didn't seem to think the queen was hot, although he did seem to have that opinion of Karina in "Citadel of Shadow" (or maybe he just had a taste for blonde babydoll types). He must have had very poor judgment when it came to girlfriends. Recall in "Child of the Stargazer" when he commisserates with Bobby, who has "lost" Uni to Kosar: "It happens to the best of us". Unless that was ego talking again, that line too hints volumes.
For all his sarcasm and complaining, Eric can be right in his assessment of things. When Dekion is healed in "Quest of the Skeleton Warrior" and flies off to find a portal, Eric dismissively says "We'll never see him again." As far as we know, he's right. He's right to complain about DungeonMaster's failure to provide a simple answer to a simple question: what's the way home. Yes, he can be an insufferable egotist, but he can also be brave, self-sacrificing and devoted to his companions. He is definitely a diamond in the rough, and you can see where he's been polished by his time in the Realm.