Spoilers for the Elsweyr and dragonhold storyline ahead
I originally hated the story that went with Kaalgrontiid, it felt way too over the top for the sake of finding another big baddy to threaten Tamriel and to bring dragons to eso just because dragons. But perhaps it was all thought out and has a major roll in elder scrolls lore, as my personal fan theory I believe Abnur Tharn and Kaalgrontiid are resurrected as one by Akatosh to become Talos.
Heres the info that lead me here
1st point worth noting is he is the first dragon to be totally destroyed, ever. Dragons in elderscrolls are immortal, their scales and flesh are removed when their soul is absorbed only by a Dragonborn. Even after so, their bones remain intact, this is not the case for Kaal, there was nothing left which means his soul is not on Tamriel and has most likely returned to Akatosh. 2nd point is his lust for domination and power over Tamriel, much like Talos. Kaalgrontiid wanted to ascend to a god, Akatosh has no reason to deny that to him but in his current form Kaalgrontiid would pose as a threat to Aludin and the natural cycle of things.
Dragonborn: The body of a mortal with the blood and soul of a dragon. Talos was Dragonborn, we do not know if Akatosh makes a new soul for a Dragonborn or if he takes the soul from a dragon and gifts it to a mortal. But if all dragons are created at the start of time it might be safe to assume the souls are reused. Talos could have inherited Kaalgrontiid's soul, it would explain a lot especially if the Dragonborn inherits the traits of the previous user of that soul. Nafaalilargus also connects the two in an odd way and is worth mentioning.
Wants to reunite Tamriel under the Empire much like Talos, Abnur was set on ending the 3 banners war no matter what the cost and his will might have carried over. Its also worth mentioning Abnur Tharn was a battlemage and is Varen's right hand man, he would have known a lot about war and tactics much like the kind Talos was innate at. Abnur also knew of the location of vital artifacts that would aid Talos like the location of the Amulet of kings and the Numidium. Talos did not know the location of these things but was eventually drawn to them almost like he knew where to look.
The exact origins of Talos are unknown but this would be my favorite if I could make it myself. What are your thoughts on this? Love it or hate it?