The Return Of The 4-D Man!

Despite making a fairly strong showing in the Mighty Thor title in the early 1970s, it seemed the character of Mercurio didn't have much future potential in further appearances. Since his obsession at the time was to locate and seize a power source that would save his dying world in another dimension, and with the god-jewel known as Xorr providing that power, Mercurio's motivation for seeking out and taking that power from our dimension by any means necessary no longer existed. As far as we could assume, Mercurio was back in his own dimension and content on his once again thriving world; in addition, he'd parted with his foe, Thor, on good terms, so it seemed his villainy had become a thing of the past.

But if that's the case, what brings him back to Earth four years later--and why is he engaging in battle with Captain Marvel?

Well, for one thing, Mercurio has made an attempt to steal knowledge from Mar-vell of the Omni-Wave projector--a Kree device which enables its user to send instantaneous messages between galaxies, but in the wrong hands can also be a deadly weapon (you have to hand it to the Kree for wanting to make what amounts to an interstellar transmitter double as one of the deadliest weapons in existence):

...but as we'll learn, writer Scott Edelman has provided Mercurio with a new lease on life as a comics villain by giving him an evil streak, which means he doesn't really need a reason beyond wanting to do evil in order to show up and cause trouble in future appearances. Welcome back to the villain fold, Mercurio!

So why is he seemingly acting in desperation here?

Apparently that energy source from the jewel didn't work out as planned--but we'll have to let Mercurio fill in the blanks for us, assuming Mar-vell is in the mood to listen to someone who's after the Omni-Wave and didn't feel like first explaining his need for it.

From the sound of it, Mercurio doesn't exactly inspire trust here, does he? But eventually he gets around to detailing his reason for returning to our dimension and seeking out Mar-vell.

It looks like Edelman has raised the stakes and revised Mercurio's predicament by indicating that his entire dimension is now endangered, rather than a single world. But as an editor's note tells us, Mercurio's story to Mar-vell may not be on the up and up--something Mar-vell verifies mere moments after he reaches Mercurio's world, evading the trap so carefully set for him.

With Mercurio revealing himself as a proud, card-carrying villain, along with his people now embracing the status of conquerors, Mercurio and his men soon find that Mar-vell is adept at dealing with both, despite their numbers. Nor do Mercurio's powers of extreme heat and cold provide any help to him, strangely enough; Thor can basically make the same claims as Mar-vell as far as being able to resist their effect, but was still visibly injured by them during their own battle.

Regardless, Mar-vell wraps this battle up faster than you can say "Omni-Wave."

When we next see Mercurio, he's apparently become an unwilling specimen of the Stranger's laboratory-world and is present when the Over-Mind launches an attack against the being who defeated his plan of universal conquest. Mercurio, along with a number of other prisoners, seizes the opportunity to make a break for freedom, even as they find themselves caught up in the conflict between the Stranger and the forces of the Over-Mind.

We learn a decade later (our time) that Mercurio was (presumably) able to escape along with others during that incident, but faced with the task of gaining the means to return to his own dimension and his world. To that end, he attempts to deceive another captain--using his former human guise of Karl Sarron to ensnare Captain America, who has his hands full dealing with an alien attempt to curtail humans' interference in stellar affairs by transforming Earth into a prison planet which will hold alien undesirables and criminals. "Sarron" offers his help in dealing with the situation--but Cap's instincts have him being suspicious from the start.

Mercurio's duplicity now out in the open and his plan in motion, Cap goes for the device holding his shield and rips out the entire assembly, forcing Mercurio to attack in order to salvage his plan. But the damage has a tragic effect on his physical state:

On a positive note, there's no longer any doubt about Mercurio's status as a recurring villain.  In fact, like any villain who suffers a horrible fate as a result of their own plan, we'll have to classify his current status as "indeterminate"--which is another way of saying that he could show up again at any time.