What's the community's thoughts on Martin? Do you think he had the ability to consume Dragons and speak their Words natually? Is there any foreshadowing or allegory supporting or denying this? I personally can't shake the feeling that he was [Dragonborn] and could Shout. Don't know why. Maybe just projecting my desire to make the CoC seem even more badass by explaining away his willing relegation to hypercompetent sidekick.

I don't think so but have nothing to back it, maybe your fantasy to be a accomplice of ldb in skyrim rather than ldb himself

He was of Dragonblood, so theoretically he would have been able to absorb a dragon's soul and shout like the player character in Skyrim.

He consumed the dragon souls from the smashed Amulet of Kings.

This is my notion as well.
If he had merely released the souls there would have been no need for his transformation, he acted as a vessel for the oversoul of the Amulet.

He was a Dragonborn (as well as all Alesdsians, Remans and Septims) and, seeing as he can wear the Amulet of Kings, so was Mankar Camoran as well it seems.
However, his role was different: he was Alduin's replacement as the dragon who rules and protects Akatosh's empire (the Empire and the Eight Divines Cult (plus Talos) seems little different the Alduin's Empire and the 8 Totems (plus Shor?)).
Mankar on other hand is like Miraak (and optionally Last Dragonborn): the Dragon seduced by a Daedric Prince to become its champion and transform Nirn from an Anuic World into a Padomayic.

A good point... but what if it is only one soul: soul of Akatosh, imprisoned by Alessia?

Well, Akatosh is still a dragon. His soul is no different than any other dragon's soul; just larger. All dragons and dragonborn are just fragments of The Dragon God of Time's soul anyway.

Mankar's wearing of the Amulet was our first indication that whatever was special about the Septims was not exclusive to the Septims. I recall back during the days of Oblivion we were all grumbling about that "obvious mistake". Indeed, the book The Refugees - which is a quasi-fictional account about the end of the Camoran Usurper and the birth of Mankar - remarks about horrible screams and wails emerging at intervals. A Bosmer identifies this as a "phantasm" employed by the Usurper to sow fear.

Now I wonder if it wasn't a Thu'um.


As for Martin - I definitely believe he's a Dragonborn and smashing the amulet released whatever was inside, thus transforming him into the Avatar of Akatosh. I suspect Martin knew this as well. His research at Cloud Ruler Temple had to turn up some connection to the Blades and the Dragonborn, after all and the smashing of the Amulet was a very deliberate act.

And don't worry about the Champion of Cyrodiil. Being awarded stewardship of an entire Daedric Realm and effective immortality and godlike powers seems like enough of a consolation prize for being "the sidekick" to me.