Easton's 1897 Bible Dictionary:

Tirhakah
   the last king of Egypt of the Ethiopian (the fifteenth) dynasty.
   He was the brother-in-law of So (q.v.). He probably ascended the
   throne about B.C. 692, having been previously king of Ethiopia
   (2 Kings 19:9; Isa. 37:9), which with Egypt now formed one
   nation. He was a great warrior, and but little is known of him.
   The Assyrian armies under Esarhaddon, and again under
   Assur-bani-pal, invaded Egypt and defeated Tirhakah, who
   afterwards retired into Ethiopia, where he died, after reigning
   twenty-six years.


Hitchcock's Bible Names Dictionary (late 1800's):

Tirhakah, inquirer; examiner; dull observer