Wow, this was a hard one, but it was some interesting research.....Alp Er Tunga has many names in Persian mythology and many conflicting and fragmented stories. Here is what i have put together:
In the Divan ul-Lughat at-Turk (Turkic dictionary) of Mahmud of Kashgar, Alp Er Tunga, is identified with the character Afrasiab in Persian literature, a descendant of the character named Tur in the Persian epic Shahnameh.
According to Shahnameh ('Book of Kings') by the Persian epic-poet Ferdowsi, Afrasiab (Alp Er Tunga) was the mythical King and hero of Turan and an archenemy of Iran. In Iranian mythology, Alp Er Tunga is considered by far the most prominent of all mythical Turanian Kings; he is a formidable warrior, a skilful general, and an agent of Ahriman who is endowed with magical powers of deception to destroy the Iranian civilization.
According to Middle-Persian and Islamic sources, Alp Er Tunga was a descendant of Tūr (Avestan: Tūriya-), one of the three sons of the Iranian mythical King Fereydun (the other two sons being Salm and Īraj). In Bundahishn he is named as the seventh grandson of Tūr. In Avestan traditions, his common epithet mairya- (deceitful, villainous) can be interpreted as meaning 'an evil man'. He lived in a subterranean fortress made of metal, called Hanakana.
According to Avestan sources, Alp Er Tunga was killed by Haoma near the Čīčhast (possibly either referring to Urmia Lake in Azarbaijan, or Lake Hamun in Sistan) and according to Shahnameh he met his death in a cave known as the Hang-e Afrasiab, or the dying place of Alp Er Tunga, on a mountaintop in Azerbaijan; the fugitive Afrasiab having been repeatedly defeated by the armies of his adversary, the mythical King of Iran Kay Khosrow (who happened to be his own grandson, through his daughter Farangis), wandered wretchedly and fearfully around, and eventually took refuge in this cave and died.