Belshazzar ruled Babylon, an intense country with a long history and a long queue of capable lords. One of those lords was Nebuchadnezzar, who had vanquished Judah, conveying the sanctuary fortunes to Babylon alongside Daniel and numerous different hostages. Belshazzar was Nebuchadnezzar's grandson through his little girl Nitocris. Belshazzar calls Nebuchadnezzar his "dad", however, this is a non-exclusive utilization of the word father, signifying "precursor."
