Mercury

Because of his tiny size, he is constantly the target of bullying, especially from Venus and sometimes from Earth. He is teased, called "squeaky," and not taken seriously. His greatest fear is that he will suffer the same fate as Pluto, who was expelled from the "club of planets"—a fear that literally paralyzes him.

He's very shy and insecure. For a long time, he had no friends at all because Venus prevented him from interacting with them. Eventually, his only "friend" was the Sun—but even here, things are complicated: Mercury is more afraid of its hot-blooded neighbor than friendly, and is always careful in conversations to avoid accidentally hurting his feelings or causing an outburst.

But don't think he's just a weak-willed victim. Mercury has a strong character inside, and he's gradually learning to show it. He genuinely sympathizes with the moons and other small celestial bodies, because he knows what it's like to be humiliated for his size.