From BiblePortal Wikipedia

Bridgeway Bible Dictionary [1]

The Cherethites and Pelethites were people who lived among the Philistines and who, like the Philistines, probably came originally from Crete ( 1 Samuel 30:14;  Ezekiel 25:16;  Zephaniah 2:5; see Philistia ). They were such good soldiers that David, upon conquering the Philistines, used them to form his personal bodyguard, under the command of the tough Benaiah ( 2 Samuel 8:18;  2 Samuel 20:23). They were fiercely loyal to David through the rebellions of Absalom and Sheba, and they supported David’s chosen successor, Solomon, when there was an attempted coup against him ( 2 Samuel 15:18;  2 Samuel 20:7;  1 Kings 1:38). There is no mention of them after the death of David.

People's Dictionary of the Bible [2]

Cherethites ( Kĕr'E-Thîtes ), Executioners, and Pelethites ( Pĕl'E-Thîtes or Pç'Leth-Îtes ), Couriers. The life-guards of King David.  2 Samuel 8:18;  2 Samuel 15:18;  2 Samuel 20:7;  2 Samuel 20:23;  1 Kings 1:38;  1 Kings 1:44;  1 Chronicles 18:17;  2 Kings 11:4, R. V. "Carites." But it has been conjectured that they may have been foreign mercenaries, and therefore probably Philistines.

International Standard Bible Encyclopedia [3]

ker´ē̇ - thı̄ts ( כּרתים , kerēthı̄m , הכּרתי , ha - kerēthı̄  ; Χελεθί , Chelethı́ "executioners," "life-guardsmen"): A people in South Palestine whose territory bordered upon that of Judah ( 1 Samuel 30:14 ). In  1 Samuel 30:16 this land is apparently identical with that of the Philistines. In   Ezekiel 25:16 the Philistines and the Cherethites are threatened together; while in   Zephaniah 2:5 the Cherethites are evidently the dwellers in "the land of the Philistines," "the inhabitants of the seacoast." Septuagint in both Ezekiel and Zephaniah renders the name "Cretans." The translators may have been "guided only by the sound." But Zeus Cretagenes in Gaza suggests a connection with the island of Crete. See, however, Caphtor . It may be taken as certain that the Cherethites were a Philistine clan. In conjunction with the Pelethites they are frequently named as forming the guard of David ( 2 Samuel 8:18 , etc.). It was the custom of many ancient monarchs to have a guard of foreign mercenaries.