Hayes Macklin is the brother of Brant Macklin, the patient in the Season 8 episode Blowing the Whistle. He is married to Joni Macklin and is the father of Evan Macklin.
Hayes was at the airport waiting for Brant to return from Afghanistan when he saw him accompanied by a squad of soldiers led by Major Mathewson. He confronted Mathewson who told Hayes that Brant had been charged with treason. Soon thereafter, Brant collapsed and was taken to hospital.
Hayes accompanied Brant to the hospital and they were soon arguing about Brant's disclosure of information about a massacre. They soon were also arguing about what their father would have done.
When Brant took a turn for the worse and refused treatment, the doctors tried to convince Hayes to start proceedings to have Brant declared incompetent, but Hayes refused. Instead, the doctors came up with a plan to have the army provide what Brant really wanted - missing pages from his father's file that would indicate why he died.
However, when the papers didn't arrive when the army said, Brant once again refused treatment. However, this time Hayes readily agreed to the court proceeding. This made Taub suspicious and he investigated. He confronted Hayes with a deception - the army had released the missing pages to Hayes, but he had refused to give them to Brant. Hayes was hiding from Brant that their father had merely died driving drunk. Brant agreed to treatment again.