Kaarthar was a nord who was told of a prophecy... The Last Few will be born... The planes of Oblivion will grow stronger... If the last few are prevented from stopping it... Tamriel will cease to exist... You are the first of The Last Few... once the last few are gathered... Talk to Paarthurnax at the throat of the world... You know what happens if you fail...
(The first two people to join will be part of the last few...)