After reading the prologue of MOI again, its clear that K'rul refers to Kallor as mortal human. That reference in the prologue to the HFE is that it had risen, and Kallor's reference to his being around when the Imass were as children is not unthinkable, when you consider that it implies that the Imass were in the dawn of their existence. Do we have to be convinced that the Imass were the progenitors of humans? Maybe what are modern humans on Malazan times are interbred of the various species that came before, and perhaps Kallor was the first tyrant king of the first line of humans, kind of an Adam-type figure. Humans could have risen at the same time as the Imass, or even before.
This seems to play into the idea of Humans rising as Tyrants. In tCG when the three remaining pure FAs are about to do battle with the Bonehunters near the end, they contemplate Tavore as being a possible "charismatic tyrant", rising "from the multitude of mediocrity that is humanity a single person of extraordinary vision conjoined with the will to achieve that vision, who presents a most formidable presence. One to shape the course of history." There has to be a first of these. And they don't necessarily have to be malicious or tyrannical in the traditional sense to have that title, although blood worship would certainly be a part things and sacrifice is most likely the source of the tyrant's power. This would somewhat play on the trope of Tolkien's Edain (sp), an original, superior line of humans, and Kallor and Serap are akin to Beren and Luthien. Dessimbelackis appears to be something like the a tyrant of that line too, and there's no reason to think that Kallor isn't the first Human to rise and eventually lead to Dessimbelackis and the HFE, which is somewhat like Numenor.
Additionally, the references in FoD to the High King are that he "built a ship", which is bad news that staggers Draconus (I'm sure we will find out why), and then Errastas and Setch talking about the High Kingdom's borders being closed to the Azathanai, and that there are "hidden truths" to the High kingdom. Neither of these references necessitate The High King being an Azathanai, nor do they rule out Kallor being the High King. Are those hidden truths, perhaps, blood worship?
The fact is, even back in MoI prologue the Azathanai understand Kallor's motive:
Quote
What of Kallor? Draconus enquired. What of this ... this creature?
We mark him, K’rul replied. We know his deepest desire, do we not?
And the span of his life?
Long, my friends.
If this takes place after his Meeting with Krin Ne Fant and the Liosan in TCG then his deepest desire is to be dead. They didn't kill him. His anger over the loss of Serap led to his mistreatment of his people, his people call down the Crippled Down, he shatters and destorys Korel but not Jacaruku or Kallor, so Kallor starts mistreating and enslaving his people destroys all his people, thus bringing K'rul into the picture. All K'rul was going to do was "snap the chains" , but soon learned Kallor killed everyone. He was probably even hoping the three elders would kill him then, and the destruction of his people was his method of invoking just that. I think Kallor in FoD liked life and loved Serap. But once she died, that was it, and he became the definitive tyrant, raising and destroying empires over and over again, as an extension of his self-hatred and desire to end his life, but not being able to die. All K'rul's curse did was age his body, as has been said before.
Forgive the length and rambling nature of this, but the three instances are related, as well as some stuff that we see in B&B, and I'm attempting to piece all the parts of this tragic and complicated character together.