Eric may be a little guy, but he's the true hero of the story. Yes, King Birtram is a good king and he does raise the cat army in order to drive away all the Nizzards in the end, but he couldn't have done so without the help (and the loyalty) that he received from his little pageboy, Eric.
Though he may be young and have a lowly position, Eric is the one character who is not afraid to question authority. When Lord Droon initially shoves the stilts at Eric and tells him to go get rid of the things, Eric doesn't just do what the Droon dude tells him, despite the fact that ol' Droon is seriously intimidating:
The King's stilts? Bury them? Eric didn't know what to think. "It will spoil all His Majesty's fun!" he stammered. (43)
He takes the time to ask why Lord Droon is having him do such a thing, even though Lord Droon is practically frothing at the mouth with impatience and anger. Even after he buries them, he changes his mind and decides that he has to go tell King Birtram about what happened. Maybe blindly following orders isn't all it's cracked up to be.
Therefore, though little and lowly (not to mention young), Eric poses the biggest threat to Lord Droon's evil plans. Through sheer bravery and a commitment to honor, Eric manages to foil Lord Droon's plan to keep King Birtram away from his beloved stilts forever.
Instead of complying with the law and staying inside the measles-marked house, Eric sneaks out, determined to reach King Birtram and help him save the kingdom:
"No time to shrink down to a boy again," thought Eric. "I'll have to stay a tall man." (102)
When he's racing toward the castle after having fooled Droon and his cronies, Eric's dogged perseverance and bravery make him the strongest character in the story. In fact, it makes him a tall (albeit a little misshapen) man.
He's the one who faces the most adversity, and he overcomes it—not for his own sake, but for the sake of his king and kingdom. In an Arthurian tale or fairytale, Eric would definitely be knighted at the end of the story for his loyalty and bravery.
But we're working with a Seuss book, here, so he gets his very own pair of stilts instead. But we're still gonna go ahead and call him Sir Eric. It has a nice ring to it, don't you think?