A tribe of Cuthites (2 syl.), driven out of Assyria by Aralius and the Shemites. They founded in Egypt a dynasty called Hyksos (shepherd kings), a title assumed by all the Cuthite chiefs. This dynasty, which gave Egypt six or eight kings, lasted 259 years, when the whole horde was driven from Egypt, and retired to Palestine. It is from these refugees that the lords of the Philistines arose. The word is compounded of hyk (king) and sos (shepherd).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Hyksos from Infoplease: