From BiblePortal Wikipedia

Morrish Bible Dictionary [1]

1. Prince of the king of Babylon; he assisted at the destruction of Jerusalem.  Jeremiah 39:3 .

2. Another prince present on the same occasion, whose title is given as Rab-mag, q.v.  Jeremiah 39:3,13 . The latter probably became the king, who was named NERIGLISSAR.He killed his brother-in-law Evil-merodach, and succeeded to the throne, B.C. 559. On some bricks his name has been found as Nergal-shar-uzur, Rubu-emga.

Hawker's Poor Man's Concordance And Dictionary [2]

Captain of Nebuchadnezzar's army, ( Jeremiah 39:3) A compound name, Ner, light-Shar, prince-Abzar, treasure.