Answer: SAL

Sal can refer to various meanings, but based on the clue provided, "sal" likely refers to Sal Paradise. Sal Paradise is the fictional alter ego and protagonist in Jack Kerouac's novel "On the Road." The book is a defining work of the Beat Generation literary movement. So, "sal" is a name referring to the character in the book.

Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Mule of old song. Explanations are generated by AI and may be inaccurate.