User blog comment:Madman97/The Aedra Vs. The Daedra theory/@comment-7953253-20131011092738/@comment-25109952-20131012120104

Alduin is a god. He is a splinter from the Oversoul Aka, and inferior to Aka-Tusk, who is the Nordic version of Aka. Heres an extract from Gamefaqs, and here is a link to that particular thread :

They're the same thing, but are also different.

Think of the Time Dragon as being a pool of water. I've used this explanation before (and it does have a few flaws), but I'll repeat it here, since it's an easy way of understanding things. Take a bucket and draw some water from that pool. This bucket of water is Alduin. Get a different, bigger bucket and draw more water from the pool. This second bucket is Akatosh.

Both buckets have the same water in them (pool water). Pour one bucket (the small one) over your garden in one big splash. This will probably wreck your garden, but clears the garden for new things to begin growing. That one is Alduin. Pour the other bucket carefully over the plants to cultivate them. That one is Akatosh.

The bigger bucket has "more" of the water in it, just as Akatosh represents "more" of the Time Dragon than Alduin does, thanks to mythopoeia. However, the first bucket is still Alduin, and it is older than the second bucket (Alduin is an older deity than Akatosh-as-we-know-him is), but the water is the same age, and comes from the same source, which means that, retroactively, they are both the same. Way back when, Alduin's bucket may well have been the biggest, and so he was the most of the Time Dragon, but that's changed since then.

Does that help? Another way of looking at Alduin and Akatosh is through Shor son of Shor, or (to use real world religion) Jesus and God, specifically the idea that Jesus is the son of God and is also God.