Board Thread:Lore Discussion/@comment-7629073-20130402085627/@comment-5989209-20140809194013

None of them are the same person:

The Eternal Champion is a well known Hero and general in the Empire

The Agent can't be the Eternal Champion because even in game, it says that the Hero doesn't meet the Emperor until after the Eternal Champion defeats Jagar Tharn. The Eternal Champion already knew the Emperor before Tharn's take over.

The Nerevarine can't be either for obvious reasons.

The Champion of Cyrodiil can't be the Nerevarine for similar obvious reasons.

And the Last Dragonborn can't be the CoC for even more obvious reasons, the CoC not being able to wear the Amulet of Kings among them.

Still, the possibility that they are all related is allowed, the Nerevarine is of a certain lineage, of course. The Heros could also all be related through Lorkhan extending this convention. As well as they are all related through the Elder Scrolls. But even given that, they are not all the same person.