Achish (?) is a name used in the Hebrew Bible for two Philistine rulers of Gath. It is perhaps only a general title of royalty, applicable to the Philistine kings. The two kings of Gath, which is identified by most scholars as Tell es-Safi, are:
The Latin transliteration "Achish" represents the "Begadkefat" aspiration over a medial stop, in later Aramaic and post-Biblical Hebrew. Before the strong influence of this dialect of Aramaic over Hebrew, which occurred after the Babylonian invasion, ? would (if the vowels are right) have been pronounced "Akîsh".
In the seventh-century B.C. Ekron inscription the name "Akîsh" appears as "son of Padi, son of Ysd, son of Ada, son of Ya'ir"; Akîsh by then held enough authority in Ekron to dedicate a temple. A similar name (IKAUSU) appears as a king of Ekron in seventh-century B.C. Assyrian inscriptions, as does Padi. Scholars agree that these two are the same men, although a royal status cannot yet be confirmed for their ancestors Ysd, Ada, and Ya'ir.
This appears to indicate that either the name "Akish" was a common name for Philistine kings, used both at Gath and Ekron, or, as Naveh has suggested, that the editor of the biblical text used a known name of a Philistine king from the end of the Iron Age (Achish of Ekron) as the name of a king(s) of Gath in narratives relating to earlier periods.
Achish king of Gath appears in the 1985 film King David, starring Richard Gere. The film differs from the Biblical story, and shows David pretending to be insane in order to gain admittance to the presence of King Achish, rather than to flee from him. David did not flee from the king.