Well this is nice, usually it takes so much longer for me to do one of these theory blogs...Regardless, you are probably pondering what there is to explain about Dark Ultramen. They are giants of darkness right? Well...no that's not wrong, but not exactly that simple either...
Dark Ultramen and Dark Giants
Now, what really and truly what grabbed my attention was lore on Dark Zagi and his origins, and that's when I noticed something about the names of Dark Ultramen. Now note, these are not 'imitation Ultras', or robotic doppelgangers, nor even monsters taking on the appearance of an Ultra. No, I'm talking about pure, one hundred percent Ultra, but evil.
In case some of you have not noticed, there is a distinct difference in the naming of some Dark Ultras. While called the Dark Giants, all three of them simply bore their name, no 'Ultraman' honorific. The Dark Giants of Nexus, bore the title 'Dark', and Lugiel, who is so very Ultra like, bares that title as well, but... the Dark versions of Seven and Ultraman, were known as Ultraseven 'Dark', Ultraman 'Dark', even Tiga's dark form was Tiga 'Dark', with the Dark coming after their name. So, I began to think, and began to notice something and like before...this theory comes down to anatomy.
The Story of Dark Zagi and his Brood
This observation starts with Zagi and his probably the linch pin for where this train of thoughts started. Now let's look at Zagi's origin. He began life as 'Ultinoid' Zagi', a construct, possibly like Terranoid from Ultraman Dyna, but built in the image of Ultraman Noa (proving again why weaponizing the power of Ultra is a bad f@#$%^g idea, people..) However, he was installed with an evolution program, that made him adapt from the foes he fought, he did this by copying their characteristics. By the time he became sentient (seriously who builds a sentient super powerful giant as a 'slave'?) he had already acquired the traits of Space Beasts.
Think about that. Zagi's biology, while based on that of an Ultra, bares the characteristics of a space beast, heck Beast the One shares several similarities with him. The One has Ultra like powers of the Travel Sphere, Human Host and Transformation, so we may know where he got it from.
Then we have his direct descendants, Faust and Mephisto. With Mephisto possessing the ability to create Beast Humans. In case you are unaware, Beast Humans, are human corpses controlled by beast cells, often in a zombie like fashion. Now question, does Mephisto simply control the cells of any Space Beast and use them or...do the cells come from him.
Now you're probably thinking, Mephisto is an 'Ultra', how would he have beast cells, well, the Ultra that made him...his biology has beast characteristics, and are we really going to assume Zagi just scrubbed the beast essence from Faust and Mephisto when he made them? I doubt that, since even when Mephisto came back 'good', he still looked the same. There is also the point that Mephisto's Arms Nexus (the bracers he and Nexus share), one was mutated to be able to turn into a claw. That's...not very Ultra like...
Long story short, Zagi and his Giants are hybrids of Ultra and Monster anatomy, which is why they are 'Dark' Giants, 'giants' in this case meaning Ultras. Granted, you can still call them Ultras, we still call Terranoid an Ultra, and he's basically a remote controlled light based robot that shoots death beams (that sounds more awesome than it should...) but under a microscope, the stuff of Zagi has more in common with Godzilla than any proper Ultra should.
The Dark Giants
Now you guys have probably figured out by now why the Dark Giants don't have the title of 'Dark' in their names. The Dark Giants, as evil as they are, and weird as some of them look (stares at Darramb's and Hudra's 'mouths'...seriously are those supposed to be mouth plates or what...?) are entirely human...until Kamila (I AM NOT SPELLING IT THE OTHER WAY EVER!!!) turned into Demonozoa...
They are not a dark mockery of what Ultras are, at least physically. Biologically, they are Ultra, 100%. However, they seem to have never been good guys, not even shown to have ever been in the Light, so they do not have the title of 'Ultraman'.
So, pure Ultras that are evil, just don't have the Ultraman Title...for the most part, but if you've seen the table of contents, you know I'm getting to him.
What is Dark Lugiel?
Now...what in Heaven's name is Dark Lugiel... That's actually not as hard as I thought it would be... Let us look at Lugiel's origins. He and Ginga were once the same being, who separated into two entities: Ginga, a giant of Light, and Lugiel a Giant of Darkness. Now...if you guys have not skipped to here, and actually paid attention to what I was saying...I shouldn't even bother typing this out, but whatever.
Lugiel is like Zagi, a hybrid of Ultra and Kaiju (or in his case probably Seijin) biological characteristics. He's a hybrid, whose non Ultra half, turns the other half dark. That generally seems to be the rule of the title. 'Dark' as a title seems to be for Ultras with monster biology mixed in and thus somehow turned to the dark side. Which means I have to explain the exception to this rule... (is it a rule, fairly sure Tsuburaya Pro will just add another Evil Ultra and just name them Dark (insert name here) even if they are pure Ultra, or vice versa...speaking of which...)
Though...thinking about it, Lugiel is more likely a Seijin with Ultra traits, as opposed to the other way around. Perhaps a moot point, but still Tsuburaya Pro, never seems to treat him as an Ultra, so maybe he is further from being a pure Ultra than even Zagi.
Ultraman Belial and other Dark Ultras.
Well...how to explain this elephant in the room...well I've been typing so far, so why not continue doing that?
Anyone who figured out what I was talking about...back at...I'm hoping with Zagi, because I don't think I was trying to be cryptic, you probably realize that...Belial...is the exception to this naming convention. Not only is Belial an evil Ultra, but he's a hybrid of Ultra and an alien species. So why is he different...well chances are, most likely the director, writer, some combination of both, or higher powers, just decided to name him 'Ultraman' Belial, to differentiate him from prior dark Ultras and/or just so people don't get confused...
Now giving them them benefit of the doubt... a lot of it, we could assume Belial got the Ultraman title, because he was shown having both previously being a pure Ultra and that he was once on the side of good. Or maybe Belial Dark, or Dark Belial, was too on the nose...
Now we go to the other Dark Ultras who bore the name Ultraman, Tiga, Seven and Ultraman. This is obvious. The 'Dark' comes after their names to show that they were once light Ultras, or to separate them from their light forms. These forms are mostly corruptions, their Ultra forms being projected under the power of darkness, with Seven and Ultraman, they were inverted images of what they originally were.
Zero Darkness was just Zero possessed byBelial, and thus a sort of Hybrid of the two (still only counts as a form for Belial)
So in Short
Dark (Insert name): This means they are an Ultra Being, with monster biology mixed in. They are not a 'pure' Ultra and are instead, in some points of view, more of monsters with very Ultra like biology. You could also see it as that being having been 'born in darkness'.
Not title: This often means they are just an Evil Ultra, a being of darkness perhaps, but most likely they were not shown as ever being good.
(Insert Name) 'Dark': Means this is a dark version of a previously good Ultra, a sort of fallen angel, to ride the angelic analogy Ultras seem to have. Basically when you see 'Dark' or some synonym at the end of the Ultra's name, think 'corrupted'.