Board Thread:Lore Discussion/@comment-6702118-20140722142914/@comment-27007772-20140722181333

Alduin is NOT actually Akatosh's first born son. Alduin origonated before him, in the past kalpas. He states this because he is in a dragon form.

At the end of each Kalpa, Alduin kills every deadra. Including Mehrunes. He kills every Aedra. He kills every mortal and every spirit. He restarts the universe.

In Skyrim, you fought Alduin in his weakest form, because he betrayed his prophecy by attempting a take over. He is not dead, however. Alduin will return in his Kalpa eating form and kill everything again, as he does countless times before.

Alduin is the strongest of all The Elder Scrolls entities.