To jump start this feature for a bit, we'll be looking at underrated characters either a side character that doesn't get much attention or from any series that's slept on starting with Moonbay.

Moonbay is a transporter, a lifestyle she's happy with singing while travelling the wasteland in her Gustav, a heavily armoured Zoid strictly made for transporting large cargo and larger Zoids making her a trucker by trade.
She would later get involved with Van's mission to bring peace to the world as team mechanic and transporter, it also helps that she already knows Irvine but always had one eye aimed at returning to her trucking after peace was made but found herself reuniting with Van and Co after the time skip where she would later be the pilot of the Ultrasaur, one of the most powerful Zoids ever constructed to stop the return of Deathsaur.
This is a great example of how best to utilize supporting characters and giving them their own motivations, Moonbay is always an upbeat happy character living her best life, a point she makes when reuniting with a rich former lover, turning down a marriage proposal because she's married to her job and because said lover has what she dubs horrible taste in music.
That's Moonbay, a free spirit who is living her best life, she's respected by all who know her and is an important character who proves pivotal to ending the conflict, Western media can learn alot from this woman.