Belshazzar, according to The Book of Daniel 5:1-2, was the descendant and successor of King Nebuchadnezzar of Babylon, the conqueror of Jerusalem. One night Belshazzar made a feast for a thousand of his lords and served them wine from the holy vessels, which his father had taken out of the Temple in Jerusalem. In answer to this sacrilege, a disembodied hand suddenly appeared writing mysterious words on the wall. Only Daniel could read them and told that the words predicted Belshazzar’s overthrow. That very night Belshazzar was slain (The Book of Daniel 5:30).
Historically Belshazzar was actually the son of Nabonidus, the third ruler after Nebuchadnessar.
See: Rembrandt. The Feast of Belshazzar.