Lang was born in New York City, the youngest child of Theresa (née Volmar, d. 2008) and Eugene Lang (1919–2017), a prominent entrepreneur and philanthropist. Lang's mother was Catholic of German and Irish descent, while his father was Jewish. Lang's paternal grandparents were Jewish emigrants from Hungary and Russia. He has two elder siblings—Jane, an attorney and activist, and David, who served as an executive at REFAC, the company their father founded in 1952. Lang's father donated much of his net worth (in excess of $150 million) to charity and did not leave an inheritance to his children, believing they each needed to learn to become self-sufficient.
