Marvin the Martian wore Roman armor, because he was based on the Roman god, Mars.
Marvin, the famous Looney Tunes character, first appeared in 1948. Chuck Jones, the animation director, saw that Bugs Bunny was outwitting Yosemite Sam and wanted to create a character that was the very opposite. He created Marvin the Martian to be quiet and soft spoken, but with actions that were very dangerous and destructive.
Marvin is different than other characters, because he is actually evil and the other characters are just daft. Unlike the other villains he’s quite clever. He was designed from a conception of the Roman god, Mars. So, they put Marvin in Roman armor and gave him an expressive body, because he had no mouth.
He comes from Mars, but is often found in other places. At first, he didn’t have a name. It wasn’t until years later when he proved to be merchandising material that they finally named him. Marvin’s image is on the Spirit rover that landed on Mars.