In the American TV series "The A Team" what is the name of "Howling Mad" Murdock's invisible dog?

Captain H. M. "Howling Mad" Murdock, played by Dwight Schultz, is a fictional character and one of the four protagonists of the 1980s action-adventure television series "The A-Team". The character of Murdock was almost written out of the series before it aired, as the producers found the character too "over the top". The popularity of the character among the test audience convinced the producers to keep the part of Murdock.

Murdock is officially declared insane when the A-Team robs the Bank of Hanoi and is committed to a psychiatric hospital. He is stated as having paranoid anxiety, delusions, and intermittent memory loss. The symptoms of his "insanity" vary from episode to episode. Murdock routinely escapes the Veterans Administration (VA) Psychiatric Hospital to accompany the A-Team on their missions. Murdock is shown playing video games and watching cartoons. He often "channels" a certain character for the duration of a mission or becomes fixated on a particular subject to the point of obsession. He also frequently refers to his invisible dog, "Billy". Despite his purported mental status, Murdock is a competent member of the team.