So what was King Zarkon's status in the Drule empire? Was he just one king in a dual\triple monarchy or what? This always confused me.

Also, if he was a Drule, why didn't he look like Hazar?

This was never clearly explained in either series. Since an Emperor ranks higher than a king, Emperor Zeppo had jurisdiction over King Zarkon. I believe in VV, the ruler of Doom was referred to as a Grand Viceroy, which may be an equivalent term/rank. The VV Drules were not thrilled that Zarkon did not bother finding worlds for them to repopulate, instead enslaving and plundering to benefit his own immediate realm. They also supported Lotor's coup towards the end of the series, so Zarkon's kingdom, some distance away from the rest of the Drule Empire, had quasi-autonomy.

As for why he looks different it was never officially explained. I have seen various fandom interpretations: a) Zarkon is an earlier Drule ancestral type, b) Hagar's magic/Doom's radiation caused him to change form, c) different species from Drule. Considering the enmity of Hazar's Drules towards Zarkon and his gang, I was always felt there was some earlier conflict, and given the Emperor is a Drule like Hazar, I felt that Zarkon's type is hierachically inferior, but this is pure conjecture on my part.

The DD comics eliminate the physical characteristics of the VV Drules, keeping the Drule name, but resembling the Doomites instead.

Of course, two different series merged together is the reason for the villain differences, but that shouldn't let WEP off the hook either Since there is no official reason, whatever you can come up with that makes sense to you is as good an explanation as any

yeah, like Lotor and Merla could easily pass as a Drule, but not Zarkon or Hagar.

From the way I always understood it, the Drule empire was ruled by Emperor Zeppo, with Planet Doom being one of the Drule Kingdoms. The difference with Zarkon was that his kingdom was a big piece of the empire & they pretty much operated on their own.

The only thing I could say about Zarkon & the Doommites is that the reason they look difference from other Drules is that the Denubian Galaxy produces different looking Drules than the Chronus Galaxy. Merla is of the Mischur race, which is totally different from the Drules, because of their cat like features. Then there's Lotor who has features which resemble more of his Chronus Galaxy counterparts, with the exception of his eyes & human-like features.

Much of this wasn't discussed in the show, but from fanfics that were written well enough to fit in with the show. They were pretty much well-drawn interpretations.

Hmmm...I guess it depends on what version of Voltron you look at.

In GoLion, Zarkon's counterpart was an Emperor, which to me signifies the top rank.

In the Image/DDP comics, he was king of the 9th Kingdom of the Drule Empire.

In Voltron, he was merely King Zarkon of the Empire of Planet Doom.

So I guess it's all a matter of intrepretation.