Definitions for "black knight"
a soldier or knight who fights for evil or at least against the monarch
The Black Knight is a fictional character in the film Monty Python and the Holy Grail. He is, as his name suggests, a black knight who guards a tiny bridge for unknown reasons. Although supremely skilled in swordplay, he suffers from unchecked overconfidence and a staunch refusal to ever give up.
A black knight is a soldier or knight who either is not bound to a specific liege or does not want his liege, or himself, to be identified and so does not bear any heraldic standards or has blackened them out.
Keywords:  hostile, takeover, bid, target, company
A company which makes a hostile takeover bid on a target company.