It says in Mysterious Akavir that Tosh Raka, leader of the Ka' Po 'Tun, became a dragon. It claims that he has black and orange scales. But how did he BECOME a dragon? Is he Dragonborn, and simply learned Dragon Aspect? Did he tame a dragon? Was he a dragon all along?

Also, it said that the Ka Po Tun plan to invade Tamriel once they beat the Tsaesci. Well, it's been over 200 years...something else must have happened because this invasion is long overdue!

His more likely a living avatar of Akatosh in some sense. As he walk like him and became him.

He probably did what the Altmer wanted to do: dracochrysalis.

My knowledge of dracochrysalis is sketchy at best though. As far as I know, it's some sort of process by which one becomes a dragon, and is the process Auriel used to ascend and the process that Auriel intended for the remaining Altmer to ascend. The current ruling Thalmor have other ideas though...

Hmm, so like an aspect, the way Alduin is an Aspect of Akatosh?

Alduin ripped himself from the oversoul. Tosh Raka became one with it. That's How I understand it. Correct me If I am wrong.

I don't think you can do that.