Attarsiya was an Ahhiyan (Achaean) warlord who lived around 1400 BC. He is known from a single Hittite text, which recounts his military activities in Western Anatolia and Alasiya. These texts are significant because they provide the earliest textual evidence of Mycenaean Greek involvement in Western Anatolian affairs. Scholars have noted potential connections between his name and that of Atreus from Greek mythology.

The Indictment of Madduwatta describes two incidents involving Attarsiya which occurred in Western Anatolia. In the first incident, Attarsiya attacked an unnamed land and forced the local warlord Madduwatta to flee. Madduwatta found refuge with the Hittite king Tudhaliya I/II who installed him as vassal ruler of Zippasla and the Siyanta River Land, territories which seem to have been located somewhere near the Arzawa Lands.

In the second incident, Attarsiya again attacked Madduwatta, this time with an army that allegedly included 100 war chariots and 1000 infantry. Attarsiya was initially victorious, though Madduwatta's Hittite backers dispatched an army under Kisnapli. The Indictment of Madduwatta gives a brief description of the battle:

Kisnapli went into battle against Attarsiya 100 [chariots and ... infantry] of Attarsiya [drew up for battle]. And they fought. One officer of Attarsiya was killed, and one officer of ours, Zidanza, was killed. Then Attarsiya turned [away(?)] from Madduwatta, and he went off to his own land.

This description has been interpreted as suggesting a duel between the two sides' champions, though it is also possible that only these two casualties were considered worthy of mention. After the battle, Attarsiya returned home and Madduwatta was reinstalled as ruler.

Later on, Attarsiya raided the island of Alashiya together with Anatolian allies including his former enemy Madduwatta. This attack alarmed the Hittites, who claimed Alashiya as a tributary but lacked the naval resources to directly control it.

Attarsiya is known solely from the Indictment of Madduwatta (CTH 147), a fragmentary Hittite text written around 1380 BC. This document, written on behalf of the Hittite king Arnuwanda I, recounts the Hittites' troubled relationship with a restive vassal named Madduwatta. Attarsiya plays a role in several episodes described in the text. When the Indictment of Madduwatta was first translated, it was assigned an erroneous date at the end of the 13th century BC. However, subsequent scholarship showed that it was in fact two centuries older based on archaic characteristics of the texts.

The Hittite account of Attarsiya's exploits provide the earliest textual evidence of Mycenaean involvement in Anatolia. These incidents are contemporary with archaeological evidence of growing Mycenaean presence at Miletus, which may have served as Attarsiya's base, as it did for later Mycenaean warlords. The Hittites' growing awareness of the Mycenaeans is attested by roughly contemporary finds from Hattusa including a Mycenaean-style sword seized from a participant in the Assuwa Revolt and a pot sherd decorated with an image that appears to depict a soldier wearing a boar's tusk helmet. In the decades after Attarsiya, Mycenaean involvement increased, to the point that the Hittite king Hattusili III even addressed the Ahhiyawan king as a peer. However, the Mycenaeans were driven out of Anatolia around 1220 BC, during the reign of Tudhaliya IV.

Attarsiya's exploits are also significant for what they reveal about the political structure of the Mycenaean world. While Linear B records suggest a number of independent Mycenaean palace-states, one potential reading of the Indictment implies that Attarsiya's army consisted of 100 chariots and 1000 infantry. Since these numbers are greater than any single Mycenaean palace-state could have mustered, some researchers such as Jorrit Kelder have argued that Ahhiyawa was an alliance or confederation.

It has been suggested by several scholars that the term Attarsiya might be related to the Greek name "Atreus", borne by a mythical king of Mycenae. However, scholars have cautioned that even if there is a connection, that does not entail that Attarsiya himself was the basis of the mythical Atreus.

Martin West proposed that Atreus is a secondary form based on the patronymic Atreïdēs, which is in turn derived from the Mycenaean *Atrehiās. This could then be derived from a preform *Atresias, *Atersias or *Atarsias, more readily connectable with Attarsiya. According to an alternative view proposed by Hittitologist Albrecht Goetze, Attarsiya could be a possessive adjective, meaning "belonging to Atreus", analogous to the typical Homeric way of referring Agamemnon and Menelaus, throughout the Iliad.

A further possible link to the grecophone sphere is the Linear B term ta-ra-si-ja, well attested in Pylian tablet series JN, a word which means "copper/bronze allotment" or "weight unit of copper/bronze", or something similar, applied to metalworkers. In the Pylos JN 415 tablet, there is also found an adjective a-ta-ra-si-jo, meaning "without copper/bronze". The context in which ta-ra-si-ja occurs during the Late Helladic period suggests that those who produced or worked with the allocated raw materials were a large work force and the work was of a low-paid status. Worth noting at Pylos around 1200 BC is the independence of a-ta-ra-si-jo smiths from allotments accorded ta-ra-si-ja smiths. It was evidently optional for anyone able to obtain sufficient quantities of copper or bronze from sources outside the palace to do so as an a-ta-ra-si-jo.