Belteshazzar’s off-ox, n. — Green’s Dictionary of Slang

Belteshazzar’s off-ox n.

[see Dan. 4:8–27, in which Daniel, also known as Belteshazzar, foretells Nebuchadnezzar’s decline into a state of ox-like stupidity]

a headstrong person.

1867

G.W. Harris Sut Lovingood’s Yarns 79: I didn’t know hit frum Beltashazur’s off-ox.