The Song of Aegwynn
The Song of Aegwynn is an epic poem about the Guardian Aegwynn's fight against Sargeras after the Burning Legion had been sent to Azeroth for the second time. Sargeras was trying to steal the power of the dragons in the frozen north. During an epic battle in which Aegwynn and the dragons fought against Sargeras and his Legion, Sargeras was seemingly defeated by Aegwynn and buried by her far beneath the sea.
The Song of Aegwynn was also used as a cipher for coded letters between Medivh and the Order of Tirisfal. Although Medivh destroyed his copy for unknown reasons before he was "killed", each member of the Order had a copy according to Medivh.