Who is…
Achish

Hebrew: אָכִ֥ישׁ —transliteration: Akish or Achish

This is the name of 2 biblical kings and is perhaps only a general title of royalty applicable to the Philistine kings.

1. Achish (aka Abimelech), the king of Gath with whom David sought refuge when he fled from Saul (1 Samuel 21:10-15)

   He is called Abimelech in the superscription of Psalm 34.

   This is probably the same king to whom David traveled a 2nd time at the head of a band of 600 warriors, and who assigned him Ziklag, with whom he carried on war against the surrounding tribes (1 Samuel 27:5-12).

   King Achish had great confidence in the valor and fidelity of David (1 Samuel 28:1-2), but at the instigation of his court advisers did not permit him to go up to battle along with the Philistine hosts (1 Samuel 29:2-11). David remained with Achish 1 year and 4 months.

2. Achish, another king of Gath, probably a grandson of the above king, to whom the 2 servants of Shimei fled

   This led Shimei to go to Gath in pursuit of them, and the consequence was that Solomon put him to death (1 Kings 2:39-46).