Wikipedia
Hartapu was a late Hittite king who likely reigned in Tarhuntassa. He is known from Hieroglyphic Luwian inscriptions from Kizildağ, Karadağ, and Burunkaya near Aksaray.
Hartapu, who bore the titles great king and hero, states himself to be the son of another great king and hero named Mursili. This Mursili likely is identical to the Hittite great king Mursili III, better known under his birth name Urḫi-Teššub, who reigned the Hittite empire in 1272-1267 BC before being dethroned by his uncle Hattusili III.
When Hartapu is the son of Mursili III, he may have succeeded his uncle Kurunta, the younger brother of Mursili III as king of Tarḫuntašša in the 2nd half of the 13th century BC. Ḫartapu's use of royal titulation may have been similar to its use by to Kurunta, who also bore the titles great king and hero to demonstrate his right to the throne of Hattusa still occupied by the descendants of the ursurper Ḫattušili III. Those descendants of Ḫattušili II were Tudhaliya IV during Kurunta's reign, and Suppiluliuma II during Hartapu's reign.
It is known that Suppiluliuma II, last known great king of Hattusa and ursurper from Hartapu's point of view, conquered Tarhuntassa during a military campaign. This may have brought Hartapu's reign to an end. Tarhuntassa may have been ruled by the great king of Hattusa again and collapsed together with the rest of the Hittite empire.
Tarhuntassa may but have survived the Hittite empire. Possible evidence is given by a Hieroglyphic Luwian inscription from Karahöyük in south-central Anatolia. In this inscriptiondated in the (later?) 12th century BC, a certain Armanani informs about a visit of a great king named Ir-Teššub in the land POCULUM, at which event the great king gave control of three cities within the country of POCULUM to Armanani. It is sure that Ir-Teššub was a great king, but his country is unknown. One hypothesis is that he was a great king of Carchemish and successor of Kuzi-Teššub. The other hypothesis is that he may in fact was a great king of Tarhuntassa. This hypothesis bases on epigraphic similarities between the inscription from Karahöyük and the inscriptions of Hartapu. This would imply that the royal line represented by Hartapu continued at least to the early Iron Age.