Pointing to a person, a man says, "His sister's father is the uncle of my wife". How is the person related to the man?

Let's break down the relationships step-by-step:"His sister's father" $\to$ A person's sister's father is simply that person's father.Substituting this back into the statement: "The person's father is the uncle of my wife."If the person's father is the uncle of the man's wife, then the person and the man's wife are first cousins (children of siblings).The cousin of a man's wife is referred to as his brother-in-law (or cousin-in-law, standardly classified under brother-in-law in competitive exams).Therefore, the person is the man's brother-in-law.