Bleep, bloop, my future Artificial Americans, and welcome to another list of comic book characters that fit into a very specific set of circumstances. In this case, it's robots. Honestly, it's a very large category to break down, so I had to cut out a lot of characters to narrow it down. So if your favorite automaton didn't make this list, maybe they'll be on the next.
10. Red Ronin
(Godzilla, Marvel Comics)
The Red Ronin, aka the SJ3RX, is a giant fighting robot that regularly bounces around the Marvel Universe punching monsters in the face.
It was originally built by SHIELD for one single purpose: Fight Godzilla. That's right, Marvel used to publish Godzilla comics. What's more, they were all in continuity. There are panels of J. Jonah Jameson shouting at Godzilla, and they are exactly as wonderful as you always assumed.
Anyway, Red Ronin started out fighting Godzilla, but because this is Godzilla we're talking about, the duo wound up teaming up a bunch later on. The Ronin fell into disrepair for a while, and eventually just became a random piece of cultural ephemera that would show up from time to time. Sunfire and Wolverine encountered it, the Wasp fought it, the Thunderbolts got some use out of it.
From what I could find, the giant robot was used by the previously mentioned Thunderbolts during the first Superhero Civil War. Hopefully, he'll make a comeback soon.