Who is Belshatzar?
Rashi: He was Nebuchadnetzar's son 1 . He ruled after Evil Merodach, who ruled in place of Nebuchadnetzar and was also his son.
Ibn Ezra (2:39, citing Rav Sadya Gaon): He was Nebuchadnetzar's grandson.
Indeed, Nebuchadnetzar is called his father (verses 11, 13, 18). However, a grandfather is called a father (Sifri Beha'alosecha 78) - "Re'u'el Avihem." We also find "Lavan ben Nachor." Yirmeyah (25:27) prophesized that all Goyim will serve Nebuchadnetzar, his son and grandson. After Belshatzar was killed, Paras and Madai seized power! Does this not prove that Belshatzar was his grandson?! (PF)
Why did he make a great feast?
Rashi citing Yosifun: That day, he fought and defeated Daryavesh ha'Midi and Koresh. At night he made a feast, like Yeshayah (21:5) prophesized "Aroch ha'Shulchan Tzafo ha'Tzafis Achol Shaso Kumu ha'Sarim" - during the feast, his enemies returned and fought against the city, and conquered it.
Malbim (from Megilah 11b): Yirmeyah's Nevu'ah that Malchus Bavel will cease after 70 years was known. They calculated that 70 years passed, and the kingship was still strong. Yosifun says that Madai and Paras came to fight him, and his 1000 officers defeated them. This showed that his Mazal was still strong! He thought that his idolatry and Sar overpowered the G-d of gods, so he made a feast for his officers.
What do we learn from "v'Lekabel Alpa Chamra Shase"?
Rashi: He drank wine corresponding to 1000 men 1 .
Ibn Ezra: He drank in front of 1000 officers - unlike the etiquette of kings. Malbim - normally, the king eats and drinks in a different room. He wanted to show their esteem in front of him, so he drank with them.
Tosfos ha'Rosh (Megilah 12b): So much wine cannot fit in a body! Rather, he drank as much wine as the biggest drinker among 1000 men.
