Prince of the small kingdom of Aritia and main character of the Fire Emblem OVA (as well as the first Fire Emblem game, whose plot the OVA describes). His character class is Lord.
His name has been translated several ways (including "Mars" and "Matus"), with "Marth" being Nintendo of America's official translation. The OVA used "Mars."
His hair is blue because, in the game, allied units are colored blue, and his hair color was picked to match.